AN  INTRODUCTION  TO 

HISTOKICAL  GEOLOGY 


WITH  SPECIAL  REFERENCE  TO 
NORTH  AMERICA 


BY 

WILLIAM    J.    MILLER 

PROFESSOR  OF  GEOLOGY,  SMrTH  COLLEGE 


238   ILLUSTRATIONS 


NEW  YORK 

D.  VAN  NOSTRAND   COMPANY 

25  PARK  PLACE 

1916 


COPYRIGHT,     IQl6,    BY 
D.    VAN     NOSTRAND     COMPANY 


3 fcO 


THE-PLIMPTON'PRESS 
NORWOOD  •  MASS  •  U  •  S-  A 


PREFACE 

IT  is  the  author's  hope  that  this  book  may  find  a  place  as  a 
class-book  dealing  with  the  historical  geology  portion  of  a  one-year 
course  in  general  geology,  and  that  it  may  also  serve  as  a  text  for 
special  courses  in  historical  geology.  An  elementary  knowledge 
of  what  is  generally  comprised  under  dynamical  and  structural 
geology  is  presupposed.  It  is  assumed  that  a  proper  amount  of 
laboratory  and  field  work  will  be  pursued  in  connection  with  the 
text. 

It  will  be  seen  that  more  introductory  space  is  devoted  to  a  dis- 
cussion of  the  broad  fundamental  principles  of  historical  geology 
than  is  customary  in  text-books.  The  experience  of  the  author 
has  been  that  careful  attention  to  these  general  principles  at  the 
beginning  of  the  subject  is  well  repaid  in  satisfaction  to  both  teacher 
and  student  when  the  great  events  of  earth  history  are  taken  up  in 
regular  order. 

A  definite  plan  is  strictly  adhered  to  in  the  discussion  of  each 
period  from  the  Cambrian  to  the  Tertiary  inclusive.  Such  defi- 
niteness  of  presentation,  in  spite  of  some  objections  which  may  be 
raised  against  it,  should  greatly  aid  the  beginner,  who  must  con- 
stantly compare  periods  and  note  the  important  changes  in  the 
evolution  of  both  land-masses  and  organisms.  The  topical  arrange- 
ments are  such  that  any  desired  comparisons  can  be  readily 
made.  A  plan  of  treatment,  the  same  for  both  the  Archeozoic 
and  Proterozoic  eras,  permits  a  ready  comparison  of  these  two. 
By  the  very  nature  of  the  subject-matter,  a  somewhat  more  special 
method  of  discussion  has  been  necessary  for  the  Quaternary  period. 

Important  features  are  the  summaries  of  Paleozoic  and  Meso- 
zoic  history  which  will  aid  the  student  in  fixing  in  mind  the  salient 
points  in  the  history  of  those  two  great  eras.  It  is  believed  that 
the  two  tabular  summaries — one  of  Paleozoic  life  and  the  other 
of  Mesozoic  life  —  will  be  helpful.  Group  by  group  and  period 
by  period,  from  the  Cambrian  to  the  Cretaceous  inclusive,  the 
principal  evolutionary  changes  in  organisms  are  brought  before 
the  student  at  a  glance  by  the  use  of  these  tables. 


360^42 


iv  PREFACE 

Students  beginning  the  study  of  geology  usually  have  either 
very  little  knowledge  of  biology  or  their  study  has  not  emphasized 
the  classification  of  organisms.  The  evolution  of  organisms  is  a 
fundamental  consideration  in  the  study  of  earth  history,  and  the 
instructor  finds  it  well-nigh  necessary  to  present  to  his  classes  out- 
line classifications  of  plants  and  animals  accompanied  by  brief 
descriptions  of  the  more  common  types.  Such  matter  is  presented 
in  the  first  chapter  of  this  book. 

In  certain  texts,  especially  those  portions  dealing  with  historical 
geology,  there  is  a  tendency  to  overwhelm  the  student  by  the  intro- 
duction of  a  multiplicity  of  technical  terms,  especially  the  names  of 
fossils.  The  present  author's  idea  has  been  to  reduce  such  terms 
to  a  reasonable  minimum  required  for  a  proper  understanding 
of  the  great  principles  of  earth  history.  The  genus  and  species 
names  accompanying  illustrations  are  given  in  the  interest  of 
scientific  accuracy  and  with  no  thought  that  these  are  to  be  re- 
membered by  the  student. 

Various  distinctly  appropriate  illustrations,  more  or  less  familiar 
because  of  their  appearance  in  other  text-books  or  manuals  of 
geology,  have  not  been  abandoned  merely  for  the  sake  of  some- 
thing new  or  different.  Many  of  the  illustrations,  however,  ap- 
pear in  a  text-book  here  for  the  first  time.  Among  the  numerous 
original  sources  of  illustrations,  particular  mention  should  be  made 
of  the  publications  of  the  United  States  Geological  Survey,  the 
New  York  State  Museum,  The  American  Museum  of  Natural 
History,  and  the  Maryland  Geological  Survey. 

The  Macmillan  Company,  Henry  Holt  and  Company, 
Ginn  and  Company,  D.  Appleton  and  Company,  and  John 
Wiley  and  Sons  have  generously  allowed  the  use  of  various 
cuts.  Careful  attention  has  been  given  to  the  selection  of 
only  such  views,  fossils,  diagrams,  and  maps  as  would  system- 
atically illustrate  the  text  without  overdoing  this  feature  of 
the  book. 

The  author  is  under  particular  obligation  to  Professor  Bailey 
Willis  of  Stanford  University  for  the  use  of  his  excellent  series  of 
paleogeographic  maps  of  North  America.  These  maps,  together 
with  his  U.  S.  G.  8.  Professional  Paper  71,  have  proved  to  be 
veritable  storehouses  from  which  to  draw  in  the  preparation  of  the 
manuscript  of  this  book. 

The  well-known  manuals  and  text-books  of  geology,  especially 


PREFACE  v 

those  by  Dana,  Chamberlin  and  Salisbury,  Pirsson  and  Schuchert, 
LeConte,  Scott,  Norton,  Blackwelder  and  Barrows,  Geikie,  Kayser, 
and  De  Lapparent,  have  been  freely  consulted,  and  due  acknowl- 
edgment is  here  made  for  the  help  derived  from  these  sources. 

Among  those  who  have  read  portions  or  all  of  the  manuscript 
are  the  following:  Dr.  J.  M.  Clarke  and  Mr.  C.  A.  Hartnagel 
of  the  New  York  State  Museum;  Professors  "W.  B.  Clark  and 
C.  K.  Swartz  and  Mr.  E.  W.  Berry  of  the  Johns  Hopkins  Uni- 
versity; and  Dr.  L.  W.  Stephenson  of  the  United  States  Geological 
Survey.  Special  acknowledgment  is  made  to  these  men  for  valu- 
able suggestions  and  criticisms,  but  the  author  holds  himself 
strictly  responsible  for  all  errors  the  book  may  contain. 

WILLIAM  J.   MILLER 

SMITH  COLLEGE, 

Northampton,  Mass., 
August,  1916 


CONTENTS 

CHAPTER  PAGE 

I.  GENERAL  PRINCIPLES 1 

II.  GENERAL  PRINCIPLES  —  CONCLUDED 23 

III.  ORIGIN  AND  PRE-GEOLOGIC  HISTORY  OF  THE  EARTH    ....  35 

IV.  THE  ARCHEOZOIC  ERA 40 

V.  THE  PROTEROZOIC  ERA 47 

"VI.  THE  CAMBRIAN  PERIOD  *. 56 

""  VII.  THE  ORDOVICIAN  (LOWER  SILURIAN)  PERIOD 77 

-  VIII.  THE  SILURIAN  (UPPER  SILURIAN)  PERIOD 103 

'  IX.  THE  DEVONIAN  PERIOD 120 

-  X.  THE  MISSISSIPPIAN  (LOWER  CARBONIFEROUS)  PERIOD    .    .    .  143 

*  XI.  THE  PENNSYLVANIAN  (UPPER  CARBONIFEROUS)  PERIOD  ...  158 

"  XII.  THE  PERMIAN  PERIOD 180 

**XIII.  SUMMARY  OF  PALEOZOIC  HISTORY  7' 194 

XIV.  THE  TRIASSIC  PERIOD 201 

XV.  THE  JURASSIC  PERIOD      219 

XVI.  THE  CRETACEOUS  PERIOD 236 

XVII.  SUMMARY  OF  MESOZOIC  HISTORY 274 

XVIII.  THE  TERTIARY  PERIOD 281 

XIX.  THE  QUATERNARY  PERioo 328 


Vll 


LIST   OF   ILLUSTRATIONS 

FIGURE  PAGE 

1.  A  Protozoan  (Amoeba)  without  a  shell.     Greatly  enlarged    ....  14 

2.  Shelled  Protozoans  (Foraminifers) 14 

3.  Sponges  on  a  shell      14 

4.  Modern  Hydrozoans.     Part  of  a  colony  much  enlarged 15 

5.  A  group  of  modern  Corals  showing  the  internal  structure  of  one 

individual 16 

6.  Stemmed  Echinoderms  (Pelmatozoans) 16 

7.  A  modern  Asterozoan  ("Starfish") .  17 

8.  Modern  Echinoids  ("Sea-urchins"),  one  with  spines  in  position  .    .  18 

9.  Bryozoans 18 

10.  Brachiopod  shells  (fossil  forms) 19 

11.  A  modern  Pelecypod 19 

12.  Gastropods 20 

13.  A  modern  chamber-shelled  Cephalopod  (Nautilus)  showing  the  in- 

ternal shell  structure 21 

14.  A  modern  Squid 21 

15.  Diagram  to  illustrate  correlation  of  rock  formations  by  continuity 

of  deposit • 24 

16.  Diagram  to  illustrate  correlation  of  rock  formations  by  similarity 

of  sequence 24 

17.  Diagram    to   illustrate   correlation   of  rock  formations  by  degree 

of  change  or  structure 25 

18.  Diagram  to  illustrate  the  significance  of  unconformities 27 

19.  A  very  symmetrical  spiral  nebula  in  Pisces  (M.  74) 37 

20.  Diagram  to  illustrate  the  formation  of  a  spiral  nebula 38 

21.  Archean  (Grenville)  sedimentary  gneiss  in  the  central  Adirondacks.  43 

22.  Map  showing  the  surface  distribution  of  pre-Cambrian  (Archeozoic 

and  Proterozoic)  rocks  in  North  America 44 

23.  Diagram  showing  the  principal  subdivisions  of  the  Proterozoic  and 

their  relation  to  the  Archeozoic  in  the  Lake  Superior  district   .    .       49 

24.  A  view  in  the  Grand  Canyon  of  Arizona  (Shinumo  quadrangle) 

exhibiting  the  relations  of  Archean,  Algonkian  and  Paleozoic  rocks 

to  each  other 52 

25.  Part  of  a  pre-Cambrian  (Huronian)  Alga 54 

26.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Cam- 

brian, and  some  very  closely  associated  Lower  Ordovician,  strata 

in  North  America  .    . 58 

27.  Geologic  section  through  northeastern  Iowa,  showing  how  character, 

thickness,  and  distribution  of  deeply  buried  rock  formations  can 

be  determined  by  a  comparison  of  well  records 60 

ix 


x  LIST    OF    ILLUSTRATIONS 

FIGURE  PAGE 

28.  Upper  Cambrian  (Potsdam)  sandstone  in  the  Ausable  Chasm  of 

northeastern  New  York 62 

29.  Paleogeographic  map  of  North  America  during  Lower  (early)  Cam- 

brian time 64 

30.  Paleogeographic  map  of  North  America  during  late  Middle  and 

Upper  (late)  Cambrian  time 66 

31.  Structure  section  in  Saratoga  County,  New  York,  showing  how 

Upper  Cambrian  strata  overlap  upon  a  hillock  of  pre-Cambrian 
rock  (Grenville) 67 

32.  Calcareous  Algae,  Cryptozoon  proliferum,  forming  a  reef  in  Upper 

Cambrian  limestone  near  Saratoga  Springs,  New  York 72 

33.  A  Cambrian  Sponge,  Leptomitus  zitteli 73 

34.  A  Cambrian  Jelly-fish,  Brooksella  alternate 73 

35.  A  Cambrian  Sponge  or  Coral,  Archeocyathus  rensselaericus    ....  73 

36.  Cambrian  Brachiopods 74 

37.  A  Cambrian  Pelecypod  (Fordilla  troyensis) 74 

38.  Cambrian  Gastropods 74 

39.  Cambrian  Trilobites,  restored  forms      75 

40.  A  Middle   Cambrian  Trilobite,  Neolemus  serratus,  with  well-pre- 

served appendages 76 

41.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  chiefly 

Middle  and  Upper  Ordovician  strata  in  North  America     ....       79 

42.  Generalized  structure  sections  through  various  parts  of  New  York 

State,  showing  the  attitude  and  relations  of  the  various  great 
rock  systems 80 

43.  The  Trenton  (mid-Ordovician)  limestone  at  its  type  locality,  Tren- 

ton Falls,  New  York 81 

44.  Geologic  (columnar)  section  in  eastern  Tennessee,  showing  the  pre- 

dominance of  limestone  in  the  Lower  and  Middle  Ordovician,  and 

of  shale  and  sandstone  in  the  Upper  Ordovician      83 

45.  Paleogeographic  map  of  North  America  during  Middle  Ordovician 

time 85 

46.  Structure  section  through  a  portion  of  the  Highlands  of  the  Hudson 

in  southeastern  New  York 87 

47.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Ordovician  time 89 

48.  Ordovician  Seaweeds,  Callithamnopsis  fructicosa 91 

49.  Ordovician  Graptolites 92 

50.  Ordovician  Echinoderms 93 

51.  Various  Ordovician  Bryozoans  on  a  slab  of  limestone 94 

52.  Ordovician  Brachiopods 95 

53.  Ordovician  Pelecypods 96 

54.  Ordovician  Gastropods 96 

55.  Ordovician  Cephalopods 97 

56.  An  Orthoceras  restored 98 

57.  Bits  of  Ordovician  sea-bottom 100 

58.  Ordovician  Trilobites 101 

59.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Silurian 

strata  in  North  America 105 


LIST    OF   ILLUSTRATIONS  xi 

FIGURE  PAGE 

60.  Paleogeographic  map  of  North  America  in  the  Silurian  period  .    .    .  109 

61.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe  dur- 

ing Silurian  time Ill 

62.  Silurian  and  Devonian  Corals     .    . 113 

63.  Silurian  Echinoderms 114 

64.  Silurian  Trilobites      115 

65.  A  Silurian  Eurypterid,  Eurypteris  remipes,  restored  to  show  dorsal 

side 116 

66.  A  Silurian  Scorpion,  Paleophonus  caledonicus 117 

67.  A  bit  of  Silurian  sea-bottom  showing  Crinoid,  Bryozoan,  Brachio- 

pod,  and  Trilobite  remains 118 

68.  Map  showing  surface  distribution  (areas  of  outcrops)  of  Devonian 

strata  in  North  America 123 

69.  Paleogeographic  map  of  North  America  during  early  Devonian 

time 126 

70.  Paleogeographic  map  of  North  America  during  Middle  Denovian 

time 127 

71.  Upper  Devonian  shales  along  the  Genesee  River  in  western  New 

York 129 

72.  Sketch  map  showing  the  general  relations  of  land  and  water  in 

Europe  during  the  Devonian 131 

73.  A  Devonian  Asterozoan,  Paleaster  eucharis,  on  a  Pelecypod  shell.  134 

74.  Devonian  Brachiopods 135 

75.  Devonian  Pelecypods 135 

76.  Devonian  Gastropods 136 

77.  A  Devonian  Goniatite,  Manticoceras  patersoni 136 

78.  Devonian  Trilobites 137 

79.  A  very  simple  Devonian  Vertebrate,  Palesopondylus  gunni   ....  137 

80.  Devonian  Ostracoderms 138 

81.  A  Paleozoic  (early  Mississippian)  Selachian  or  Shark,  Cladoselache 

fyleri 139 

82.  Devonian  Fishes , 139 

83.  Structure  of  a  Ganoid  tooth 140 

84.  Types  of  Fish  tails 141 

85.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Missis- 

sippian and  Pennsylvanian  strata  in  North  America      .....  145 

86.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Mis- 

sissippian strata  in  eastern  North  America 146 

87.  Paleogeographic  map  of  North  America  in  Mississippian  time  .    .    .  149 

88.  Generalized  section  in  Iowa,  showing  how  the  Pennsylvanian  sys- 

tem (C)  rests  unconformably  upon  the  Mississippian  (M)     .    .    .  150 

89.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Mississippian  (Lower  Carboniferous)  time 151 

90.  Mississippian  Cup-corals,  Lonsdaleia  canadense,  forming  a  compact 

mass  or  colony 154 

91.  A  Mississippian  Blastoid  head,  Pentrimites  elongatus      155 

92.  A  Mississippian  Crinoid  head,  Forbesiocrinus  wortheni 155 

93.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Penn- 

sylvanian rocks  in  eastern  North  America 159 


xii  LIST   OF    ILLUSTRATIONS 

FIGURE  PAGE 

94.  Geologic  structure  section  through  one  of  the  anthracite  coal 

fields  of  eastern  Pennsylvania 160 

95.  Geologic  (columnar)  section  in  western  Pennsylvania  showing  the 

vertical  distribution  of  coal  beds  (heavy  black  bands)  and  their 
relations  to  associated  strata 162 

96.  Paleogeographic  map  of  North  America  during  Pennsylvanian  time     165 

97.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Pennsylvanian  (Upper  Carboniferous)  time 167 

98.  Lepidodendron  bark  (a)  and  Sigillarian  bark  (6),  showing  arrange- 

ment of  leaf  scars 170 

99.  Fronds  of  a  Pennsylvanian  Fern,  Mariopteris 171 

100.  A  Living  Tree-fern      172 

101.  A   Permo-Carboniferous   landscape,    showing   some   of   the  most 

conspicuous  plants  of  the  great  Coal  Age 173 

102.  A  Cycadofilices  or  Seed-fern 174 

103.  Cordaites  restored 175 

104.  A  Pennsylvanian  Goniatite 175 

105.  Pennsylvanian  Eucrustaceans 176 

106.  Pennsylvanian  Arachnids 176 

107.  A  Pennsylvanian  Insect,  Corydaloides  scudderi  (Brogniart)    ....  177 

108.  A  Pennsylvanian  Amphibian  (Labyrinthodont),  Eryops 178 

109.  Transverse  section  of  a  Labyrinthodont  tooth 179 

110.  Late  Permian  or  early  Triassic  "Red  Beds"  in  Red  Butte,  eastern 

Wyoming , 182 

111.  Paleogeographic  map  of  North  America  during  latest  Paleozoic 

(Permian)  time 184 

112.  Highly    generalized    structure    sections    across    the   Appalachian 

Mountains  and  adjoining  districts  to  illustrate  certain  impor- 
tant features  in  the  history  of  the  region 186 

113.  Structure  section  through  a  portion  of  the  Appalachian  Moun- 

tains of  western  Virginia  showing  the  typical  deformation  of 
Paleozoic  strata 187 

114.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  later  Permian  time 189 

115.  A    Permian    chambered    Cephalopod,     Waagenoceras    cumminsi 

(White),  showing  highly  folded  suture  (partition)  lines    ....  191 

116.  A  Permian  Reptile,  Pareiasaurus  serrideus 192 

117.  A  Permian  Reptile  (Pelycosaurian),  Naosaurus  claviger 192 

118.  Highly  generalized  paleogeographic  map  of  North  America  during 

the  Paleozoic  era 196 

119.  Map  showing  the  surface  attribution  (areas  of  outcrops)  of  Triassic 

and  Jurassic  strata  in  North  America 202 

120.  Structure  section  across  the  Triassic  basin  of  the  Connecticut 

Valley  near  Northampton,  Mass.,  showing  the  tilted  and  faulted 
character  of  the  rocks 203 

121.  Tilted  and  faulted  Triassic  sandstone  in  the  Connecticut  Valley  near 

Northampton,  Mass 204 

122.  Columnar  (geologic)  section  showing  ages,  character  and  thickness 

of  strata  in  northeastern  Wyoming 205 


LIST   OF   ILLUSTRATIONS  xiii 

FIGURE  PAGE 

123.  Paleogeographic  map  of  North  America  during  Triassic  time  .    .    .     207 

124.  The  steep  western  front  of  the  Holyoke  Range  as  seen,  from  East- 

hampton,  Massachusetts 209 

125.  Sketch  map  showing  the  relation  of  land  and  water  in  Europe  in 

the  early  Triassic 211 

126.  Parts  of  a  Triassic  Conifer,  Voltzia  heterophylla 213 

127.  A  Triassic  Ceratite,  Ceratites  trojanus,  with  part  of  shell  removed 

to  show  suture  structure 214 

128.  A  Triassic  long-tailed  Macruran  Decaped,  Pemphix  Sueurii    .    .    .     215 

129.  A  Ganoid,   Catopterus   redfieldi,  from    the  Triassic    sandstone    of 

Connecticut 216 

130.  Tracks  of  a  small  two-legged  Dinosaur  on  a  slab  of  Triassic  sand- 

stone from  the  Connecticut  Valley 216 

131.  Tracks  of  a  large  two-legged  Dinosaur  on  Triassic  sandstone  from 

the  Connecticut  Valley,  showing  how  both  feet  slid  some  dis- 
tance in  the  soft  material  after  which  the  creature  suddenly  sat 
down,  the  end  of  the  backbone  having  left  a  distinct  impression.  217 

132.  Structure  section  through  a  portion  of  the  central  Sierra  Nevada 

Mountains,  exhibiting  the  highly  folded  character  of  the  Jurassic 

and  late  Paleozoic  rocks 220 

133.  Paleogeographic   map   of   North   America    during    late   Jurassic 

time 222 

134.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  late  Jurassic  time 224 

135.  A  living  Cycad,  Dioon  edule,  of  Mexico 226 

136.  A  fossil  Cycad  tree  trunk,  Cycadeoidea  pulcherrima 227 

137.  Jurassic  Cycad  leaves 228 

138.  A  Jurassic  Crinoid,  Pentacrinus  fossilis 229 

139.  A    regular    or    radially    symmetrical    Echinoid,    Pseudodiadema 

texanum,  of  Lower  Cretaceous  age 229 

140.  An  irregular  or  bilaterally  symmetrical  Echinoid,  Hemiaster  tex- 

anus,  of  Cretaceous  age 230 

141.  An  Ammonite  with  part  of  shell  removed  to  show  the  very  com- 

plicated (frilled)  sutures 230 

142.  Internal  shell  of  a  Belemnite,  restored 231 

143.  A  Jurassic  Belemnite,  Belemnoteuthis  antiqua 231 

144.  A  Jurassic  long-tailed  Decapod  (Macruran) 232 

145.  Three  stages  in  the  life  history  of  a  modern  Crab 233 

146.  A  primitive  or  ancestral  Jurassic  Teleost,  Hypsocormus  insignis     .  233 

147.  The  earliest  known  Bird,  Archeopteryx  macrura,  from  the  Jurassic.  234 

148.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Lower 

Cretaceous  strata  in  North  America 238 

149.  Map   showing   the   surface   distribution    (areas   of   outcrops)    of 

Upper  Cretaceous  strata  in  North  America 239 

150.  Paleogeographic  map  of  North  America  during  Lower  Cretaceous 

time 245 

151.  Paleogeographic  map  of  North  America  during  Upper  Cretaceous 

time 247 

152.  Typical  exposure  of  Upper  Cretaceous  (Selma)  chalk  in  Alabama.      248 


xiv  LIST    OF   ILLUSTRATIONS 

FIGURE  PAGE 

153.  Structure  section  across  Nebraska  from  the  Rocky  Mountains  to 

Omaha 249 

154.  Structure  section  in  the  Rocky  Mountains  of  western  Montana 

showing  moderate  folding  of  Cretaceous  and  older  rocks  ....     250 

155.  Diagrammatic  section  through  the  Atlantic  slope  at  about  the  lati- 

tude of  northern  New  Jersey,  showing  the  structures  and  rela- 
tions of  the  various  physiographic  provinces  as  they  now  exist.     251 

156.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Lower  Cretaceous  time 253 

157.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  early  Upper  Cretaceous  time 254 

158.  Cretaceous  Foraminifers,  greatly  enlarged 257 

159.  A  Cretaceous  Brachiopod,  Terebratula  harlani 257 

160.  Typical  Cretaceous  Pelecypods 259 

161.  Typical  Cretaceous  Ammonites 260 

162.  A  Cretaceous  Teleost  Fish,  Osmeroides  Lewesiensis,  restored       .    .  261 

163.  A  Cretaceous  toothed  Bird,  Ichthyornis  victor 262 

164.  A  group  of  Ichthyosaurs,  Ichthyosaurus  quadricissus,  of  the  Enalio- 

saur  division  of  Mesozoic  Reptiles 264 

165.  A  well-preserved  Ichthyosaur  found  in  Germany      265 

166.  A  restored  Plesiosaur,  Plesiosaurus  dolichodeirus,  of  the  Enaliosaur 

division  of  Mesozoic  Reptiles 266 

167.  A  Mosasaur,  Tylosaurus  dyspelor,  of  the  Enaliosaur  division  of 

Mesozoic  Reptiles 267 

168.  The  hugest  of  all  known  Dinosaurs,  a  Sauropod,  Diplodocus  .    .    .  268 

169.  A  Stegosaur,  an  armored  Dinosaur 269 

170.  A  Triceratops,   Triceratops  prorsus,  of  the  Dinosaur  division  of 

Mesozoic  Reptiles 269 

171.  Theropods,  Allosaurus  agilis,  of  the  Dinosaur  division  of  Mesozoic 

Reptiles 270 

172.  A  small  two-legged  Dinosaur,  Podokesaurus  holyokensis  from  the 

Triassic  of  Massachusetts 271 

173.  An  Ornithopod,  Claosaurus  annectens,  of  the  Dinosaur  division  of 

Mesozoic  Reptiles 272 

174.  A    Rhamphorhynchus    of    the    Pterosaur    division    of    Mesozoic 

Reptiles 272 

175.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Lower 

Tertiary    (Eocene   and   Oligocene)    strata   in   North   America.     283 

176.  Map  showing  the  surface  distribution  (area  of  outcrops)  of  Upper 

Tertiary  (Miocene  and  Pliocene)  strata  in  North  America  .    .    .     285 

177.  Eocene  sandstone  resting  by  sharp  contact  upon  Upper  Cretaceous 

white  chalk  in  Alabama 286 

178.  Eocene-Oligocene  strata  as  seen  in  the  Wind  River  Basin  of 

Wyoming 288 

179.  Soft  wn*ite  diatomaceous  Miocene  shale  in  southern  California.     290 

180.  Paleogeographic  map  of  North  America  during  Lower  Tertiary 

(Eocene-Oligocene)  time 293 

181.  Paleogeographic  map  of  North  America  during  Miocene  time    .    .     295 

182.  ''Toadstool  Park  " :  a  view  in  the  Bad  Lands  of  western  Nebraska.     266 


LIST    OP    ILLUSTRATIONS  xv 

FIGURE  PAGE 

183.  Structure  section  across  a  portion  of  the  Coast  Range  Mountains 

of  central-western  California,  showing  the  character  of  the  Ter- 
tiary folding  and  faulting 297 

184.  Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Tertiary 

and  later  volcanic  rocks  in  North  America 302 

185.  Structure  section  in  central  Washington  showing  sheets  of  Miocene 

lava  piled  up  to  a  thickness  of  fully  a  mile 303 

186.  Mount  Lassen  in  northern  California  in  eruption  August  22,  1914.  304 

187.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Middle  Eocene  time 306 

188.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Middle  Pliocene  time 307 

189.  Sketch  map  showing  the  relations  of  land  and  water  in  Europe 

during  Middle  Pliocene  time 308 

190.  Diatoms  from  diatomaceous  earth  of  Tertiary  age 311 

191.  A  well-preserved  fossil  Palm,  Thrimax  eocenica,  from  the  Eocene 

of  Georgia 312 

192.  An  Eocene  Foraminifer,  Nummulina  levigata 313 

193.  Large  Oyster  shells,  Ostrea  georgiana,  in  Eocene  strata  of  Georgia.  314 

194.  Tertiary  Pelecypods 315 

195.  Tertiary  Gastropods 315 

196.  A  nearly  perfect  fossil  Teleost  Fish,  Diplomystus  densatus,  from 

the  Eocene  of  Wyoming 316 

197.  A  Shark's  tooth  from  the  Eocene  of  the  Gulf  Coastal  Plain    ...  317 

198.  Head     of     an    Eocene    Bird,    Odontopteryx    toliapicus,    showing 

teeth 317 

199.  Sketches  to  illustrate  increase  in  size  of  brains  of  Mammals  from 

the  Eocene  to  the  present 318 

200.  A  nearly  perfect  skeleton  of  the  Eocene  Phenacodus  primaevus  .    .  319 

201.  Chart  to  illustrate  the  evolution  of  the  Horse  family 320 

202.  Primitive  or  ancestral  Horses,  Eohippus,  of  the  Eocene 321 

203.  Evolution  of  foot  of  even-toed  (Artiodactyl)  Mammals  illustrated 

by  existing  forms .- 322 

204.  a,  Mastodon  tooth;  6,  Mammoth  tooth      322 

205.  A  Mammoth  Elephant,  Elephas  primigenius 323 

206.  Chart  to  illustrate  the  evolution  of  the  Elephants 324 

207.  Skeleton  of  an  Eocene  Creodont,  Patriofelis 326 

208.  One  of  the  earliest   Monkeys,   Mesopithecus  pentelici,  from  the 

Miocene  of  Europe 326 

209.  Map  showing  the  areas  occupied  by  ice  in  North  America  at  the 

time  of  maximum  glaciation 330 

210.  Diagram  to   show  how  successive  glacial  drift  sheets  are  dis- 

tinguished   333 

211.  Smoothed  and  striated  (glaciated)  limestone 335 

212.  Structure  section  across  the  Black  River  Valley  of  northerA  New 

York,  to  illustrate  the  effect  of  ice  erosion  and  glacial  lake  dis- 
position    336 

213.  Typical  drumlins  (side  view)  in  western  New  York 339 

214.  A  group  of  kames  in  New  York  state 340 


xvi  LIST    OF    ILLUSTRATIONS 

FIGURE  PAGE 

215.  First  stage  in  the  history  of  the  Great  Lakes,  when  all  the  rest  of 

the  lake  basins  were  still  buried  under  the  ice 343 

216.  Lake  Whittlesey  stage  of  the  Great  Lakes  history,  when  the  eastern 

and  western  ice-margin  lakes  combined  with  outlet  past  Chicago.  344 

217.  Glacial  Lake  Warren 345 

218.  Glacial  Lakes  Duluth,  Chicago  and  Lundy 346 

219.  The  Algonquin-Iroquois  stage  of  the  Great  Lakes,  with  outlet 

through  the  Mohawk-Hudson  Valleys  of  New  York 347 

220.  The  Nipissing  Great  Lakes  and  their  correlatives 349 

221.  Sketch  map,  of  central  New  York,  showing  the  relation  of  the  pre- 

Glacial  drainage  to  that  of  the  present 352 

222.  Sketch  map  of  the  southeastern  Adirondack  region,  showing  the 

relation  of  the  pre-Glacial  drainage  to  that  of  the  present     .    .    .  353 

223.  Sketch  map  of  the  Niagara  River  gorge 354 

224.  Pre-Glacial  drainage  of  the  Upper  Ohio  River  Basin 355 

225.  Pre-Glacial   drainage    (dotted   lines)    of   a   part   of   northwestern 

,  Illinois 356 

226.  Diagram  showing  effect  of  Precession 362 

227.  Map  showing  extent  of  the  extinct  Lakes  Bonneville    (a)    and 

Lahontan  (6)  in  the  western  United  States 367 

228.  Map  showing  the  extent  of  ice  in  Europe  at  the  time  of  maximum 

glaciation 368 

229.  A  great  Ground-sloth,  Megatherium  americanum 369 

230.  Great  armored  Glyptodonts,  Doedicurus  clavicaudalus  and  Glyp- 

todon  clavipes 370 

231.  Table  to  show  the  principal  geologic,  stages  in  the  history  of 

Man 374 

232.  Comparison  of  skull  profiles  of  lowest  types  of  Men  and  highest 

Apes 375 

233.  Restoration  of  the  head  of  Pithecanthropus  erectus 375 

234.  Comparison  of  skulls 376 

235.  A  charging  wild  Boar,  one  of  the  best  paintings  by  Paleolithic 

Man  in  the  cave  at  Altimira,  Spain 379 

236.  The  "Procession  of  Mammoths"  ;  a  painting  by  Paleolithic  Man 

in  a  cave  at  Font-de-Gaume  in  west-central  France 380 

237.  Line  cut  copy  of  a  Paleolithic  painting  in  the  cave  at  Cogul,  Spain.     380 

238.  Map  of  the  United  States  showing  the  principal  physiographic 

provinces  frequently  referred  to  in  the  text 382 


HISTOEICAL   GEOLOGY 

WITH   SPECIAL   REFERENCE   TO   NORTH 
AMERICA 

CHAPTER  I 

GENERAL    PRINCIPLES 

WHAT  HISTORICAL  GEOLOGY  TEACHES 

HISTORICAL  geology  deals  with  the  evolution  of  earth  struc- 
tures and  organisms.  Its  object  is  to  arrange  the  events  of  earth 
history  in  the  regular  order  of  their  occurrence.  The  records  of 
these  events  are  preserved  in  the  rocks  of  the  crust  of  the  earth, 
the  layers  (strata)  of  which  have  been  likened  to  the  leaves  of  a 
great  book.  Many  times  the  pages  of  this  vast  " nature-book" 
contain  remarkable  records  and  illustrations,  while  at  other 
times  they  are  comparatively  barren.  In  order  that  the  reader 
may,  at  the  outset,  form  some  general  idea  of  the  scope  and  char- 
acter of  the  subject,  the  following  summary  of  the  more  important 
conclusions  derived  from  the  study  of  earth  history  is  here  presented. 

Inorganic  Inferences.  —  1.  The  age  of  the  earth  must  be  meas- 
ured by  at  least  tens  of  millions  of  years.  One  great  mountain  range 
after  another  has  been  built  up  and  then  worn  away  by  the  ordi- 
nary processes  of  erosion.  Many  thousands  of  feet  (in  thickness) 
of  strata  have  been  accumulated  by  the  deposition  of  sediments 
slowly  derived  by  the  removal  of  thousands  of  feet  of  materials 
from  the  lands.  Such  facts  force  us  to  the  inference  of  a  vast 
antiquity  for  the  earth. 

2.  The  physical  geography  of  the  earth  has  been  notably  different 
in  earlier  geological  time  from  that  of  the  present.  For  example, 
many  millions  of  years  ago  (during  the  Ordovician  period)  an  inte- 
rior sea  spread  over  much  of  what  are  now  the  Mississippi  Valley 
and  the  Appalachian  Mountain  regions,  as  well  as  regions  still 
farther  westward. 

1 


2  HISTORICAL  GEOLOGY 

3.  All,  or  nearly  all,  of  the  surface  of  the  lithosphere  has  at  some 
time,  or  times,  been  covered  by  sea  water.    Stratified  rocks  of  marine 
origin  now  constitute  fully  five-sixths  of  the  exposed  surface  of 
the  lithosphere,  and  it  is  certain  that  from  most,  at  least,  of  the 
remaining  surface  such  stratified  rocks  have  been  removed  by 
erosion. 

4.  The  continents  were  roughly  outlined  in  early  geologic  time. 
This  is  proved  by  the  facts  that  even  the  oldest  known  rocks  con- 
tain much  land-derived  sediment  of  comparatively  shallow  water 
origin  and  that  there  are  no  deposits  which  show  that  great  oceanic 
abysses  ever  extended  across  what  are  now  continental  areas. 
Much  evidence  points  to  a  very  early  development  of  oceanic 
basins  and  continental  masses  which  have  occupied  essentially  the 
same  positions  to  the  present  time. 

5.  During  geologic  time  there  has  been  a  progressive  tendency 
for  the  continental  masses  to  become  higher  and  broader.    There  have 
been  many  oscillations  of  level,  accompanied  by  transgressions  or 
retrogressions  of  the  sea,  but  the  processes  of  elevation  (relatively 
speaking)  have  been  predominant,  while,  at  the  same  time,  the  sea 
bottoms  have  become  narrower  and  deeper.     Just  prior  to  the  last 
Ice  age,  and  only  a  short  time  ago,  geologically  considered,  North 
America  was  even  higher  and  broader  than  at  present,  for  then  the 
shallow  marginal  sea  bottoms  (continental  shelves)  were  also  dry 
land. 

Organic  Inferences.1 —  1.  Organisms  inhabited  the  earth  many 
millions  of  years  ago.  All  but  possibly  the  very  oldest  known  series 
of  rocks  contain  organic  remains. 

2.  Throughout  the  known  history  of  the  earth   organisms  have 
continuously  changed.     Each  epoch  of  earth  history  or  series  of. 
strata  has  its  characteristic  assemblage  of  animals  and  plants. 
The  more  ancient  strata  contain  no  species  like  those  living  to- 
day, the  latter  being  found  only  in  rocks  of  comparatively  (geo- 
logically) recent  date.    Further,  "the  organisms  which  inhabited 
the  earth  during  any  geological  epoch  were  descended  from  organ- 
isms of  preceding  epochs"  (W.  H.  Norton). 

3.  The   change  in  organisms  has  been  progressive.     In  early 
geological  time  the  animals  and  plants  were  comparatively  simple 
and  low  in  the  scale  of  organization  and  structure,  and  through  the 

1  These  statements  of  organic  inferences  follow,  in  the  main,  Norton's 
Elements  of  Geology. 


GENERAL  PRINCIPLES  3 

succeeding  epochs  higher  and  more  complex  types  were  gradually 
developed  until  the  highly  organized  forms  of  the  present  time, 
culminating  in  man,  were  produced.  It  should  be  remembered, 
however,  that  not  all  change  in  organisms  has  been  progressive, 
but  rather  only  a  single  thread. 

4.  No  species   once  extinct  has  ever  reappeared.     Numerous 
important  species  have  lived  through  many  epochs  ;of  geologic 
time,  while  others  have  had  only  brief  existence.      In  no  case, 
however,  has  a  species  once  become  extinct  been  known  to  re- 
appear. 

5.  While  higher  and  higher  types  have  been  developed  during 
geologic  time,  many  of  the  earlier  and  simpler  types  have  persisted. 
Thus  Foraminifers,   which  are  exceedingly  simple,   single-celled 
animals,  have  lived  in  the  sea  from  early  geologic  time  to  the 
present. 

6.  The  broader  or  larger  biological  groups  of  organisms  have 
persisted  longer  than  the  smaller.     No  subkingdom  has  ever  become 
extinct,  though  species  frequently  have  not  outlived  even  a  single 
geological  epoch.     As  a  rule,  genera  have  survived  longer  than 
species,  orders  longer  than  genera,  etc. 

7.  The  life  history  of  the  individual  tends  to  recapitulate  the 
evolution  or  history  of  the  race.     A  Frog,  which  is  a  typical  Am- 
phibian, shows  certain  fish-like  characters  during  its  embryonic  de- 
velopment, as,  for  example,  the  presence  of  gills  and  tail.    Again, 
the  modern  Crab,  which  is  a  Crustacean,  shows  a  gradual  shorten- 
ing of  the  tail  portion  during  its  embryonic  development.     The 
earliest  known  Crustaceans  were  practically  all  long  tailed. 

FOSSILS   AND    THEIR    SIGNIFICANCE 

Traces  or  remains  of  plants  and  animals  preserved  in  the  rocks 
are  known  as  fossils.  The  term  originally  referred  to  anything 
dug  out  of  the  earth,  whether  organic  or  inorganic,  but  for  many 
years  it  has  been  strictly  applied  to  organisms.  Paleontology, 
which  literally  means  ''science  of  ancient  life,"  deals  primarily 
with  fossils. 

Darwin  thought  that  the  stratified  rocks  contain  only  a  very 
incomplete  record  of  the  geologic  history  of  life.  Though  many 
thousands  of  species  of  fossils  have  been  described  from  rocks  of  all 
ages  except  the  very  oldest,  and  more  are  constantly  being  brought 


4  HISTORICAL  GEOLOGY 

to  light,  it  must  be  evident  that,  even  where  conditions  of  fossili- 
zation  were  most  favorable,  only  a  small  part  of  the  life  of  any 
period  is  represented  by  its  fossils.  Comparatively  few  remains 
of  organisms  now  inhabiting  the  earth  are  being  deposited  under 
conditions  favorable  for  their  preservation  as  fossils.  So  it  has 
been  throughout  the  long  periods  of  earth  history,  though  the  fossils 
in  the  rocks  known  and  unknown  are  a  fair  average  of  the  groups 
of  organisms  to  which  they  belong.  In  spite  of  such  imperfec- 
tions in  the  life  record,  it  is,  nevertheless,  remarkable  that  so  vast 
a  number  of  fossils  are  embedded  in  the  rocks,  and  from  these  we 
are  enabled  to  draw  many  fundamental  conclusions  regarding  the 
history  of  life  on  our  planet. 

Preservation  of  fossils.  —  1.  Preservation  of  the  entire  organism 
by  freezing.  Fossilization  by  this  method  is  rare,  though  remark- 
able examples  are  afforded  by  extinct  species  of  the  Mammoths 
and  Rhinoceroses,  the  bodies  of  which,  with  flesh,  hide,  and  hair 
intact,  have  been  found  in  frozen  soils  in  Siberia. 

2.  Preservation  of  the  entire  organism  by  natural  embalmment. 
Fine  examples  are  the  perfectly  preserved  Insects  in  the  famous 
amber  of  the  Baltic  Sea  region.     This  amber  is  a  hardened  resin, 
the  Insects  having  been  caught  in  it  while  it  was  still  soft  and  exud- 
ing from  the  trees. 

3.  Preservation  of  only  the  hard  parts  of  the  organisms.     This  is 
a  very  common  kind  of  fossilization  in  which  the  soft  parts  have 
disappeared  by  decomposition,  while  the  hard  parts,  such  as  bones, 
shells,  etc.,  remain.     Fossils  of  this  kind  are  abundant  in  rocks  of 
later  geological  time,  though  original  shell  material  is  frequently 
found,  even  in  very  ancient  rocks. 

4.  Preservation  of  carbon  only  (carbonization) .     This  is  particu- 
larly true  of  plants  where,  as  a  result  of  slow  chemical  change  or 
decomposition,  the  hydrogen  and  oxygen  mostly  disappear,  leav- 
ing much  of  the  carbon,  but  with  the  original  structure  often 
beautifully  preserved.     Many  excellent  examples  are  furnished 
by  the  fossil  plants  of  the  great  coal  (Pennsylvanian)  age. 

5.  Preservation  of  original  form  only  (casts  and  molds) .     Fossils 
of  this  class,  which  are  very  abundant,  show  none  of  the  original 
material,  but  only  the  shape  or  form  has  been  preserved.     When 
a  fossil  becomes  embedded  in  sediment,  which  hardens  around  the 
entire  organism  or  any  part  of  it,  and  the  organism  then  decom- 
poses or  dissolves  away,  a  cavity  only  is  left  and  this  is  called  a 


GENERAL  PRINCIPLES  5 

mould.  A  cast  may  be  formed  by  filling  a  mould  with  some  sub- 
stance such  as  sediment  or  mineral  matter  carried  by  underground 
water,  or  by  filling  a  hollow  organism  like  a  shell  with  some  solid 
substance.  The  cast  reproduces  the  internal  form  of  the  shell  or 
organism.  Frequently  original  shell,  mould,  and  cast  may  be  seen 
in  a  single  specimen,  while  more  commonly  the  original  shell  has 
been  dissolved  away.  Only  in  rare  instances  have  casts  of  wholly 
soft  animals,  or  the  soft  parts  of  other  animals,  such  as  the  Jelly- 
fishes  and  Cuttle-fishes,  been  found  in  ancient  rocks. 

6.  Preservation  of  original  form  and  structure   (petrifaction). 
Here  again  we  have  a  common  kind  of  fossilization.     When  a  plant 
or  hard  part  of  an  animal  has  been  replaced,  particle  by  particle, 
by  mineral  matter,  we  have  what  is  called  petrifaction.     Often 
organic  matter,  such  as  wood,  or  inorganic  matter,  such  as  a  car- 
bonate-of-lime  shell,   have  been  so  perfectly  replaced  that  the 
original  minute  structures  are  preserved  as  in  life.      Conditions 
favorable  for  the  petrifaction  of  flesh  seem  never  to  have  ob- 
tained. 

7.  Preservation  of  tracks  of  animals.     Footprints  of  animals, 
made  in  moderately  soft  mud  or  sandy  mud  which  soon  hardens 
and  becomes  covered  with  more  sediment,  are  especially  favorable 
for  preservation.     Thousands  of  examples  of  tracks  of  great  ex- 
tinct Reptiles  have  been  found  in  the  red  sandstone  of  the  Con- 
necticut River  Valley  alone.     Tracks  or  trails  of  Clams  or  similar 
animals,  and  burrows  of  Worms,  are  also  not  uncommon  in  the 
ancient  rocks  of  the  earth. 

Rocks  in  which  Fossils  occur. — 1.  Land  deposits.  Old  soils 
sometimes  contain  bones  or  other  organic  remains.  Peat-bogs  are 
especially  favorable  for  the  preservation  of  fossils,  as,  for  example, 
the  wealth  of  plants  directly  associated  with  the  resulting  coal 
seams;  remains  of  animals,  such  as  Frogs,  Snakes,  etc.,  which 
inhabited  the  swamp  or  bog;  and  the  bones  of  other  animals  which 
wandered  in  and  became  entombed.  Cave  deposits  often  cover 
animal  remains,  many  bones  of  extinct  animals,  even  including 
prehistoric  Man  and  the  things  he  used,  having  been  found  in  such 
deposits.  Wind-blown  deposits,  like  dune-sand,  loess,  and  desert 
deposits,  may  contain  plant  or  animal  remains.  Interglacial  de- 
posits sometimes  contain  fossils,  as,  for  example,  the  layers  of 
vegetable  matter  with  occasional  bones  of  animals  found  in  the 
interglacial  deposits  of  the  upper  Mississippi  Valley.  Lavas 


6  HISTORICAL  GEOLOGY 

rarely  contain  fossils,  but  volcanic  ash  deposited  in  water  may 
be  rich  in  organic  remains,  this  being  especially  true  of  certain 
portions  of  the  western  interior  of  the  United  States. 

2.  River  and  lake  deposits.     River  deposits  often  carry  river 
forms  themselves,  or  land  forms  which  fell  into  the  stream  and  be- 
came entombed  in  its  deposits.     Lakes  offer  very  favorable  con- 
ditions for  fossilization.     " Surrounding  trees  drop  their  leaves, 
flowers,  and  fruit  upon  the  mud-flats,  Insects  fall  into  the  quiet 
waters,  while  quadrupeds  are  mired  in  mud  or  quick-sand  and  soon 
buried   out   of  sight.     Flooded   streams  bring  in   quantities   of 
vegetable  debris,   together  with  the  carcasses  of  land  animals 
drowned  by  the  sudden  rise  of  the  flood  "  (W.  B.  Scott). 

3.  Marine  deposits.     By  far  the  largest  number  and  variety 
of  organic  remains  are  found  in  rocks  of  marine  origin,  because  on 
the  sea  bottom  the  conditions  for  their  preservation  have  been 
most  favorable.     The  distribution  of  fossils  in  strata  of  marine 
origin  is,  however,  exceedingly  irregular,  ranging  from  those  strata 
which  are  almost  entirely  made  up  of  fossils  to  others  which  are 
nearly  barren.     Longshore  deposits  are  usually  not  rich  in  fossils, 
because  of  the  grinding  action  of  the  waves,  while  deposits  formed 
in  the  quiet  waters  off  shore  often  contain  vast  numbers  of  fossils. 
Many  conditions  have  produced  great  diversity  in  the  distribution 
of  marine  organisms  throughout  known  geologic  time:   tempera- 
ture, depth  of  water,  supply  of  food,  degree  of  salinity,  nature  of 
the  sea  bottom,  clearness  of  the  water,  etc.     The  oldest  fossiliferous 
strata  seem  to  contain  practically  no  land  forms,  probably  because 
land  forms  were  but  slightly,  if  at  all,  developed  so  early.     In 
marine  strata  of  more  recent  date  terrestrial  organisms  are  often 
found,  especially  in  delta  deposits,  where  such  remains  have  been 
swept  into  the  sea  at  the  mouths  of  rivers. 

Significance  of  Fossils.  —  It  would  be  difficult  to  overestimate 
the  value  of  fossils  in  the  study  of  earth  history.  They  furnish 
most  important  evidence  regarding  earth  chronology,  ancient 
geographic  and  climatic  conditions,  as  well  as  a  basis  for  a  proper 
understanding  of  the  evolution  relations  and  distribution  of  modern 
organisms.  Leonardo  da  Vinci  (1452-1519),  the  famous  artist, 
architect,  and  engineer,  while  engaged  in  canal  construction  in 
northern  Italy,  saw  many  fossils  embedded  in  the  rocks.  He  con- 
cluded that  these  organisms  had  actually  lived  in  marine  water 
which  once  spread  over  the  region.  William  Smith  (1769-1839) 


GENERAL  PRINCIPLES  7 

of  England  was,  however,  the  first  to  recognize  the  fundamental 
significance  of  fossils  for  determining  the  relative  ages  of  stratified 
rocks.  His  announcements,  based  upon  much  careful  detailed 
work,  were  made  in  the  latter  part  of  the  eighteenth  century  and 
the  early  part  of  the  nineteenth  century.  He  has  been  called  by 
the  English  the  "Father  of  Historical  Geology." 

1.  Earth  chronology.  In  any  given  region  the  best  way  to 
learn  the  relative  ages  of  the  stratified  rocks  is  to  determine  their 
"  order  of  superposition,"  the  general  assumption  being  that  the 
older  strata  underlie  the  younger  because  the  underlying  sediments 
must  have  been  first  deposited.  While  this  is  a  fundamental 
method,  it  is  very  limited  in  its  application  when  used  alone  in 
regard  to  the  construction  of  the  whole  earth's  history.  The  suc- 
cession of  strata  seen  in  any  one  locality  or  region  represents  only 
a  small  part  of  the  earth's  entire  series  and  this,  taken  in  connec- 
tion with  the  fact  that  the  lithologic  character  of  strata  of  the  same 
age  frequently  changes,  makes  it  clear  that  "order  of  superposi- 
tion" alone  will  not  suffice  to  determine  the  relative  ages  of  sedi- 
mentary rocks  on  a  single  continent  or  even  large  portion  of  a 
continent,  not  to  mention  the  utter  inadequacy  of  the  method 
when  applied  to  comparing  the  relative  ages  of  strata  of  different 
continents. 

"Order  of  superposition,"  however,  when  used  in  connection 
with  the  fossil  content  of  the  strata,  furnishes  us  with  the  method 
of  determining  earth  chronology.  "Life,  since  its  introduction  on 
the  globe,  has  gone  on  advancing,  diversifying,  and  continually 
rising  to  higher  and  higher  planes  .  .  .  Accepting,  then,  the  un- 
doubted fact  of  the  universal  change  in  the  character  of  the  organic 
beings  which  have  successively  lived  upon  the  earth,  it  follows  that 
rocks  which  have  been  formed  in  widely  separated  periods  of 
time  will  contain  markedly  different  fossils,  while  those  which  are 
laid  down  more  or  less  contemporaneously  will  have  similar  fossils. 
This  principle  enables  us  to  compare  and  correlate  rocks  from  all 
the  continents  and,  in  a  general  way,  to  arrange  the  events  of  the 
earth's  history  in  chronological  order  ...  A  geological  chronology 
is  constructed  by  carefully  determining,  first  of  all,  the  order  of 
superposition  of  the  stratified  rocks,  and  next  by  learning  the  fossils 
characteristic  of  each  group  of  strata  .  .  .  The  order  of  succes- 
sion among  the  fossils  is  determined  from  the  order  of  super- 
position of  the  strata  in  which  they  occur.  When  that  succession 


8  HISTORICAL  GEOLOGY 

has  been  thus  established,  it  may  be  employed  as  a  general 
standard."  1 

The  student  should  bear  in  mind  that  strata  cannot  be  deter- 
mined as  precisely  contemporaneous,  because  geologic  time  has 
been  very  long  and  the  evolution  of  organisms  very  slow,  and  al- 
most exactly  similar  fossils  may  be  expected  in  strata  showing  an 
age  difference  of  at  least  some  thousands  of  years.  Also,  at  any 
given  ancient  time  of  earth  history,  as  now,  organisms  were  not  the 
same  in  all  parts  of  the  world,  so  that  rocks  formed  at  exactly  the 
same  time  in  different  parts  of  the  world  always  show  certain 
differences  in  fossil  content.  As  compared  with  the  vast  length 
of  geologic  time,  however,  practical  contemporaneity  of  the  strata 
can  usually  be  determined. 

An  excellent  example  of  well-marked  differences  in  the  distri- 
bution of  organisms  over  a  comparatively  limited  area  during  one 
of  the  ancient  epochs  of  earth  history  has  been  worked  out  by 
J.  M.  Clarke.  During  the  Portage  epoch  of  the  Devonian  2  period 
an  arm  of  the  sea  or  gulf  extended  over  much  of  the  southern  part 
of  New  York  state,  and  "the  distinctions  in  the  life  provinces  over 
the  north  shore  of  this  ancient  gulf  are  marked  with  wonderful 
clearness.  No  such  striking  illustration  of  distinct  faunal  associa- 
tions in  an  area  of  so  slight  extent  is  elsewhere  afforded  by  the 
rocks  of  New  York."  3 

For  the  determination  of  geologic  chronology,  certain  organisms 
are  more  valuable  than  others,  the  best  being  those  which  have  had 
wide  geographic  distribution  and  short  geologic  range.  For 
example  marine  organisms,  which  live  near  the  ocean  surface 
(so-called  pelagic  forms)  and  are  easily  distributed  over  wide  areas, 
while,  at  the  same  time,  the  species  are  extant  for  only  a  compara- 
tively short  time,  are  the  best  chronologic  indicators.  The  Grap- 
tolites  of  the  early  Paleozoic  era  furnish  excellent  illustrations. 

2.  Past  physical  geography  conditions.  Typical  stratified  rock 
occupying  any  region  proves  the  former  presence  of  water  over  that 
region.  By  the  study  of  the  fossils  we  can  further  usually  tell 
whether  the  water  was  ocean  or  lake,  fresh  or  salt,  open  sea  or  arm 

1  W.  B.  Scott:    An  Introduction  to  Geology,  2nd   Edition,  pp.  521-522 
and  525. 

2  The  subdivisions  of  geologic  time  are  tabulated  near  the  end  of  chap- 
ter 2. 

3  J.  M.  Clarke:  N.  Y.  State  Mus.  Memoir  No.  6,  1903,  p.  209. 


GENERAL  PRINCIPLES  9 

of  the  sea,  deep  or  shallow,  close  to  or  far  from  land,  etc.  Litho- 
logic  character  alone  may  give  some  idea  as  to  the  depth  of  water 
and  proximity  to  land  where  a  given  stratum  was  deposited,  but 
the  presence  of  considerable  numbers  of  terrestrial  organisms  gives 
important  additional  data.  Thick  limestones  filled  with  fossil 
Corals  point  to  long-continued  conditions  of  clear  sea  water.  Tree 
stumps,  on  the  other  hand,  with  roots  still  in  their  original  position, 
plainly  prove  a  former  land  surface.  By  means  of  fossils,  many 
land  areas  have  been  proved  to  have  existed  as  effective  barriers  to 
migrations  of  marine  organisms.  Certain  lands  now  separated  by 
water  may  be  shown  to  have  been  formerly  connected,  as  was  true 
of  Alaska  and  Siberia,  by  a  land  connection  across  Bering  Strait. 
Also  the  fossils  found  in  the  rocks  of  the  Isthmus  of  Panama  show 
that  North  and  South  America  were  there  connected  at  a  compara- 
tively recent  time  in  earth  history. 

3.  Past  climatic  conditions.  Some  strata  afford  an  idea  of 
the  climatic  conditions  under  which  they  were  laid  down.  Thus 
salt  and  gypsum  beds,  more  or  less  associated  with  certain  red 
sandstones  or  shales,  indicate  an  arid  climate  at  the  time  of  their 
formation.  But  the  study  of  fossils  is  much  more  fruitful  in  this 
connection.  Certain  strata  in  southern  England  contain  fossil 
Palms,  Gourds,  Crocodiles,  etc.,  thus  proving  a  subtropical  climate 
for  the  time  of  their  origin.  Other  strata,  representing  a  later 
date  in  southern  England,  carry  remains  of  Arctic  animals  and 
hence  indicate  a  cold  climate  for  that  time.  The  finding  of 
Walrus  remains  in  New  Jersey  and  Musk-ox  remains  in  Arkansas 
indicate  a  former  colder  climate  for  those  regions.  Again,  many 
fossil  Palms,  Ferns,  and  other  temperate  to  subtropical  plants,  as 
well  as  animals,  clearly  point  to  former  warmer  climate  in  those 
same  regions. 

Much  strong  evidence  for  climatic  conditions  over  various  por- 
tions of  the  earth  during  different  geologic  periods  has  been  fur- 
nished by  the  study  of  true  marine  organisms.  Certain  kinds  of 
Corals  live  only  in  shallow  tropical  seas,  and  so,  if  in  any  region 
we  find  a  bed  of  limestone  rich  in  Corals  of  this  kind,  it  is  to  be  in- 
ferred that  this  limestone  was  formed  in  warm,  shallow  sea  water. 
Such  coral  limestones  are  known  even  in  the  interior  of  North 
America. 

In  deducing  climatic  inferences,  as  above  explained,  certain 
care  must  be  exercised,  because  we  are  not  justified  in  assuming  that 


10  HISTORICAL  GEOLOGY 

because  a  given  species  now  lives  under  warm  climatic  conditions, 
every  species  of  the  same  genus  has  lived  under  similar  conditions. 
When,  however,  we  are  dealing  with  species  still  living,  or  in  older 
rocks,  with  whole  groups  of  organisms  pointing  to  certain  climatic 
conditions,  we  are  reasonably  safe  in  our  inferences. 

4.  Relations  and  distribution  of  modern  organisms.  It  is  evi- 
dent that,  if  we  are  to  properly  understand  the  present-day  rela- 
tions and  distribution  of  organisms,  we  must  learn  about  their 
ancestry  and  history,  because  all  modern  plants  and  animals  have 
directly  descended  from  those  which  lived  in  earlier  geologic  epochs. 
In  many  cases  existing  plants  or  animals,  notably  different  in 
structure,  can  be  traced  back  to  a  common  ancestry.  Again,  cer- 
tain peculiarities  in  the  distribution  of  some  of  the  present-day  ani- 
mals are  readily  explained  in  the  light  of  their  geologic  ancestry 
and  habitats.  A  good  example  is  Australia,  where  practically  all 
of  the  present-day  Mammals  (barring  those  introduced  by  Man) 
are  of  very  simple  types,  that  is,  non-Placentals  such  as  the  Kanga- 
roo, Spiny  Ant-eater,  etc.,  found  only  in  and  close  to  Australia,  and 
which  are  clearly  much  more  like  the  Mammals  of  distinctly  earlier 
geologic  time  than  like  typical  Mammals  of  the  present  day.  The 
explanation  is  that  Australia  was  separated  from  Eurasia  before 
the  higher  (Placental)  Mammals  had  been  evolved,  and  that  the 
very  different,  or  probably  much  less  severe,  struggle  for  existence 
in  isolated  Australia  has  not  been  favorable  for  the  evolution  of 
Placentals  as  was  the  case  elsewhere. 

OUTLINE  CLASSIFICATIONS  OF  ANIMALS  AND  PLANTS 

Since  a  knowledge  of  the  classifications  of  animals  and  plants 
and  the  principal  characteristics  of  the  more  important  groups  of 
organisms  is  a  fundamental  consideration  in  the  study  of  the  life 
of  each  period,  and  in  understanding  the  bearings  of  these  life 
records  upon  the  great  doctrine  of  organic  evolution,  outline  classi- 
fications of  plants  and  animals,  with  simple  explanations,  are  here 
given.  The  classifications  are  necessarily  very  brief,  and  no  great 
degree  of  biologic  refinement  is  intended.  Rather  the  purpose  is 
to  have  a  convenient  arrangement,  essentially  in  biologic  order,  of 
the  principal  groups  of  organisms  to  form  a  simple  basis  for  the 
discussion  of  the  life  of  each  period  of  geologic  history  as  presented 
in  this  text-book. 


GENERAL  PRINCIPLES 


11 


Organisms  are  divided  into  many  groups,  such  as  kingdoms 
(e.g.  plant  and  animal),  subkingdoms,  branches,  classes,  orders, 
genera,  and  species.  A  species  is  "the  smallest  group  of  plants  or 
animals  having  certain  characters  in  common  that  make  them 
different  from  all  other  plants  or  animals"  (G.  W.  Hunter). 
Species  are  grouped  together  into  larger  subdivisions  called  'genera 
(singular  "  genus"),  etc.  The  scientific  name  of  an  organism  gen- 
erally consists  of  two  words  —  the  first  signifying  the  genus  and 
the  second  the  species,  as,  for  instance,  "  Archeopteryx  macroura," 
which  literally  means  "  primitive  winged  creature  with  a  long  tail," 
and  is  the  name  of  the  earth's  first  known  Bird. 


Plants.  — 
I.  CEYPTOGAMS 


II.  PHANEROGAMS 


1.  Algae  (e.g.  Sea-weeds  and  Diatoms). 

kl.  Thallophytes   \  2.  Fungi  (e.g.  Mushrooms). 
2.  Bryophytes     (e.g.  Mosses), 
f  1.  Lycopods  (e.g.  Club-mosses). 
3.  Pteridophytes  {  2.  Equiseta?  (e.g.  Horse-tails). 
[  3.  Filiees  (e.g.  Ferns). 

(Cycadofilices,  e.g.  Seed-ferns). 
1.  Cycads. 

1.  Gymnosperms     2.  Cordaites. 

3.  Conifers  (e.g.  Pines,  Spruces,  etc.). 

1.  Monocotyledons  (e.g.  Grasses,  Lil- 

2.  Angiosperms  ies,  etc.). 

2.  Dicotyledons  (e.g.  Oaks,  Roses,  etc.). 


I.    The  CRYPTOGAMS  comprise  all  of  the  flowerless  and  seedless 
plants,  the  reproductive  organs  being  single  cells  called  spores. 

1.  Thallophytes  show  "no  definite  axis  of  upward  growth,  and 
no  distinction  of  root,  stem,  and  leaf.     They  all  consist  entirely 
of  cellular  tissue,  being  entirely  destitute  of  wood"  (J.  D.  Dana). 
In   general   there  are  two  groups  of  Thallophytes  —  Algae  and 
Fungi  —  the  former  containing  chlorophyl  and  able  to  live  upon 
inorganic  substances,  while  the  latter  are  without  chlorophyl  and 
live  upon  organic  matter. 

2.  Bryophytes  are  like  Thallophytes  in  being  woodless,  but  they 
develop  a  sort  of  axis  of  upward  growth  and  possess  leafy  stems. 

3.  Pteridophytes  (Fig.    101)    comprise   the   highest   types  of 
non-flowering  plants,  and  these  have  a  clear  distinction  of  root, 
leaf,  and  stem,  the  stem  possessing  woody  fibres.     These  plants 
have  been  much  more  favorable  for  fossilization  than  most  of  the 
foregoing,  and  they  assume  considerable  importance  in  the  fossil 


12  HISTORICAL  GEOLOGY 

forests,  especially  of  the  great  Coal  (Pennsylvanian)  age.  (1)  Lyco- 
pods  usually  have  branching  stems  upon  which  are  crowded 
numerous  small,  single-nerved,  needle-like  leaves.  Modern  repre- 
sentatives are  the  small  " Ground-pines"  or  " Club-mosses " 
so  familiar  as  Christmas  decorations.  (2)  Equisetce  have  erect 
growth,  hollow  or  pithy  segmented  stems,  and  leaves  arranged  in 
whorls  around  the  stems.  (Fig.  101.)  Modern  representatives 
are  the  " Horse-tails,"  which  are  rush-like  plants  often  seen  along 
our  streams.  Both  Lycopods  and  Equisetse  grew  to  be  large  trees 
during  the  great  Coal  (Pennsylvanian)  age.  (3)  Filices  or  Ferns 
of  temperate  climates  usually  have  fronds  springing  from  a  buried 
stem,  while  tropical  forms  may  have  fronds  arranged  around  the 
summit  of  tree-like  trunks. 

Cycadofilices  are  fern-like  plants  (Fig.  102)  which  have  been 
recently  recognized  as  a  group  seemingly  intermediate  between  the 
highest  Cryptogams  (i.e.  Filices)  and  the  lowest  Phanerogams 
(i.e.  Cycads).  They  possess  seeds  but  not  true  flowers,  and  show 
certain  other  characters  intermediate  between  Ferns  and  Cycads. 
These  plants  are  all  extinct,  but  from  the  fossil  and  evolution  stand- 
points they  are  important. 

II.  PHANEROGAMS  comprise  the  seed-bearing,  flowering  plants 
whose  reproductive  organs  are  stamens  and  pistils  and  whose  seeds 
contain  embryo  plants. 

1.  Gymnosperms  or  the  so-called  "naked  seed"  plants  include 
all  those  which  do  not  have  their  seeds  inclosed  in  a  case  or  ovary. 
They  possess  very  simple  flowers,  and  their  mode  of  growth  is 
exogenous.1  (1)  Cycads  are  palm-like  in  appearance  (Fig.  135), 
certain  of  them  being  erroneously  called  "Sago  Palms."  True 
Palms,  however,  are  Angiosperms  with  endogenous  growth.  In 
some  ways  Cycads  also  resemble  the  Ferns.  Though  now  un- 
common, the  Cycads  are  of  considerable  geological  importance. 
(2)  Cordaites  (Fig.  103)  are  now  entirely  extinct,  but  during  the 
latter  part  of  the  Paleozoic  era  they  grew  extensively  as  tall,  slender 
trees  "with  trunks  rising  to  great  height  before  branching,  and 
bearing  at  the  top  a  dense  crown,  composed  of  branches  of  various 
orders,  on  which  simple  leaves  of  large  size  were  produced  in  abun- 

1  Exogenous  plants  grow  from  without;  have  distinct  bark,  wood,  and 
pith;  and  show  concentric  rings  of  growth,  a  new  ring  usually  being  added 
each  year.  Endogenous  plants  grow  from  within  and  have  neither  pith  nor 
concentric  rings  of  growth. 


GENERAL  PRINCIPLES 


13 


dance"  (D.  H.  Scott).  (3)  Conifers  include  the  familiar  Pines, 
Spruces,  etc.,  all  of  which  have  dense,  cone-like  clusters  of  very 
simple  flowers. 

2.  Angiosperms  all  have  their  seeds  enclosed  in  a  case  or  ovary, 
and  have  more  highly  developed,  typical  flowers  as  well  as  greater 
complexity  than  the  Gymnosperms.  (1)  Monocotyledons,  such 
as  the  familiar  Palms,  Grasses,  Lilies,  etc.,  produce  only  a  single 
leaf  from  the  germinating  seed,  are  endogenous,  and  usually  have 
parallel- veined,  simple  leaves.  (2)  Dicotyledons,  such  as  Oaks, 
Roses,  and  many  other  familiar  plants,  produce  two  leaves  from 
the  embryo,  are  exogenous,  and  usually  have  net-veined  leaves. 


Sub-kingdoms 
I.   PROTOZOANS. 
II.    PORIFERS  (e.g.  Sponges). 

III.     CCELENTERATES. 


Animals.1 

Classes 


1.  Rhizopods 

2 

3 

4... 


1.  Foraminifers  (calcareous 

shelled). 

2.  Radiolarians  (siliceous  shelled) . 

Not  fossil. 


1.  Hydrozoans  (e.g.  Jelly-fishes,  Graptolites) . 

2.  Anthozoans  (e.g.  Corals). 


IV.    ECHINODERMS. 


(  1.  Cystoids  (Bladder-like  forms).. 

1.  Pelmatozoans.  <>  2.  Blastoids  (Bud-like  forms). 

3.  Crinoids  (Lily-like  forms). 

1.  Ophiuroids  (e.g.  Brittle-stars). 

2.  Asteroids  (e.g.  common  Star-fishes). 

1.  Echinoids  (e.g.  Sea-urchins). 

2.  Holothuroids  (e.g.  Sea-cucumbers). 


2.  Asterozoans. 

3.  Echinozoans. 


V.    VERMES  (e.g.  Worms).     Not  important  as  fossils. 

VI.     MOLLUSCOIDS. 


VII.     MOLLUSKS. 


1.  Bryozpans  (e.g.  Sea-mosses). 

2.  Brachiopods  (e.g.  Lamp-shells).  ^ 

1.  Pelecypods  tfe.g.  Oysters,  Clams). 


2. 
3... 


Not  common  as  fossils. 


4.  Gastropods  £e.g.  Snails) .  ^ 

'  (  1.  Tetrabranchs  (e.g. 

5.  Cephalopoda]  2.  „££$&.«.  Squids, 


fishes). 


Ammonites, 


Cuttle- 


VIII.   ARTHROPODS. 


IX.    VERTEBRATES. 


1.  Merostomes  (e.g.  Horse-shoe 
Crabs). 

1.  Crustaceans.  -I  2.  Trilobites.   t— 

3.  Eucrustaceans  (e.g.  Crabs, 
Lobsters) . 

2.  Arachnids  (e.g.  Spiders,  Scorpions,  Eurypterids). 

3.  Myriapods  (e.g.  Centipedes). 

4.  Insects  (e.g.  Grasshoppers,  Flies). 

1.  Ostracoderms  (e.g.  Armor-fishes). 

2.  Fishes. 

3.  Amphibians  (e.g.  Frogs,  Salamanders). 

4.  Reptiles  (Lizards,  Snakes). 

5.  Birds. 

6.  Mammals  (e.g.  Dog,  Man). 

This  classification  is  after  Zittel  with  certain  modifications  and  omissions. 


14 


HISTORICAL  GEOLOGY 


Fig.  1 

A  Protozoan  (Amoeba)  without  a 
shell.  Greatly  enlarged.  (From 
Shimer's  "  Introduction  to  the 
Study  of  Fossils,"  courtesy  of 
The  Macmillan  Company.) 


Fig.  2 

Shelled  Protozoans  (Foramin- 
ifers).  (From  Shimer's  "In- 
troduction to  the  Study  of 
Fossils,"  courtesy  of  The 
Macmillan  Company.) 


I.  PROTOZOANS  are  the  simplest  of  all  animals.  They  consist 
of  single  cells  of  protoplasm  and  are  without  distinct  organs.  Rhi- 
zopods  are  the  only  Protozoans  which  are  encased  in  shells,  the 


Fig.  3 

Sponges  on  a  shell.     (Courtesy  of  the  American 
Museum  of  Natural  History.) 


GENERAL  PRINCIPLES 


15 


Foraminifers  having  carbonate  of  lime  shells  and  the  Radiolarians 
shells  of  silica.  Though  very  small,  these  shells  have  frequently 
built  up  limestone  (chalk),  or  chert  beds. 

II.  PORIFERS  or  SPONGES,  which  are  the  simplest  of  the  many- 
celled  animals,  are  sac-like  forms  supplied  with  numerous  pores 
or  canals  through  which  water  containing  food  circulates  to  feed 
the  cells.     Distinct  organs  are  lacking.     Most  Sponges  have  either 
siliceous  or  calcareous  skeletons. 

III.  CCELENTERATES  are  also  very  simple  many-celled  animals, 
but  they  possess  distinct  mouth,  body  (or  stomach)  cavity,  and 
usually  have  radiating 

tentacles  surrounding 
the  mouth.  The 
canal  system  of  the 
Sponges  is  absent. 
Hydrozoans  are  little 
creatures  consisting  of 
tube-like  sacs  with 
mouth  at  one  end 
surrounded  by  ten- 
tacles. Anthozoans  are 
very  much  the  same, 
but  have  a  more  or 
less  distinct  esopha- 
gus, and  have  the 
body  cavity  divided 

by  radiating  vertical 

Fig.  4 

Modern  Hydrozoans.  Part  of  a  colony  much 
enlarged.  (From  Schuchert's  "Historical 
Geology,"  permission  of  John  Wiley  and 
Sons.) 

the  former,  the  Graptolites  (now  extinct)  are  numerous  and  im- 
portant in  early  Paleozoic  rocks,  while  the  latter  or  Corals  have 
always  been  prominent  since  pretty  early  geologic  time. 

IV.  ECHINODERMS  possess  a  distinct  body  cavity  which  con- 
tains the  digestive  or  alimentary  canal,  distinct  nervous  system, 
and  a  water  circulatory  system.     Most  Echinoderms  are  radi- 
ally segmented  and  protected  by  shells.     1.  Pelmatozoans  are  char- 
acterized by  having  segmented  stems  by  which  they  are  attached 
to  the  sea-floor  or  some  object  during  at  least  part  of  their  existence. 


partitions.  Some  Hy- 
drozoans and  Antho- 
zoans colonize  and 
some  do  not.  Among 


16 


HISTORICAL  GEOLOGY 


Fig.  5 

A  group  of  modern  Corals  showing  the  internal  structure  of  one  individual. 
(After  Pfurtscheller,  from  Schuchert's  "Historical  Geology,"  permission 
of  John  Wiley  and  Sons.) 

Among  Pelmatozoans,  the  Cystoids  are  small,  bladder-like  forms 
with  irregular  radial  arrangement  of  plates  of  the  shell  and  arms 


6  c 

Fig.  6 

Stemmed  Echinoderms  (Pelmatozoans).     a,  Cystoid,  6,  Blastoid, 
c,  Crinoid. 


GENERAL  PRINCIPLES 


17 


wholly  absent  or  only  slightly  developed;  the  Blastoids  are  bud- 
like  forms  with  plates  of  the  shell  in  very  regular  radial  order,  and 
without  arms;  and  the  Crinoids  are  lily-like  forms  with  regular 
radial  arrangement  of  plates  of  the  shell,  and  with  long,  feathery 
arms  surrounding  the  mouth.  2.  Aster ozoans  are  the  free-moving, 
star-shaped  Echinoderms  usually  with  five  arms  or  rays  radiating 


Fig.  7 

A  modern  Asterozoan  ("Starfish")-  (From  Shimer's  "Intro- 
duction to  the  Study  of  Fossils,"  permission  of  The  Mac- 
millan  Company.) 

from  a  central  disk.  Of  these  the  Ophiuroids  (Brittle-stars)  have 
slender,  flexible  rays  very  distinct  from  the  central  disk,  while  the 
Asteroids  have  thicker  rays  not  so  sharply  separated  from  the 
central  disk,  and  the  alimentary  canal  extends  into  the  rays. 
3.  Echinozoans  are  not  free-moving,  are  without  free  arms,  and 
are  stemless.  Of  these  the  Echinoids  (Sea-urchins)  have  hard 
shells  made  up  of  calcareous  plates  usually  immovably  joined  and 
covered  with  numerous  movable  spines;  and  the  Holothuroids 


18 


HISTORICAL  GEOLOGY 


(Sea-cucumbers)  are  soft  bodied,  with  leathery  covering,  tentacles 
around  the  mouth,  and  skeletons  of  scattering  limey  spicules. 


B 


Fig.  8 

Modern  Echinoids  ("Sea-urchins"),  one  with  spines  in  position.  (After 
Coe,  from  Schuchert's  "Historical  Geology,"  permission  of  John  Wiley 
and  Sons.) 

V.  VERMES  or  WORMS  include  a  large  group  of  forms  more 
complex  in  organization  than  the  preceding  groups.  Some  are 
segmented  and  others  are  not.  Since  hard  parts  are  very  rarely 
developed,  the  Worms  are  of  no  great  importance  as  fossils,  their 


Fig.  9 

Bryozoans:  A,  portion  of  modern  colony  seen  from  above  (x!5);  C,  an 
individual  expanded;  D,  fossil  form.  A-C  after  Verrill  and  Smith; 
D,  from  Ulrich.  (From  Shimer's  "Introduction  to  the  Study  of  Fossils," 
permission  of  The  Macmillan  Company.) 

presence  usually  being  indicated  by  trails,  burrows,  or  tubes  made 
in  mud  or  sand. 

VI.   MOLLUSCOIDS,  as  the  name  suggests,  bear  a  resemblance 
to  the  Mollusks.    They  differ  from  the  Anthozoans,  Echinoderms, 


GENERAL  PRINCIPLES 


19 


Worms,  and  Arthropods  in  the  entire  absence  of  body  segmenta- 
tion. Absence  of  distinct  head  and  foot,  the  lower  development 
of  the  nervous  system,  and  usual  lack 
of  locomotive  power  distinguish  them 
from  Mollusks.  A  highly  characteristic 
feature  of  the  Molluscoids  is  a  sort  of 
collar,  or  pair  of  arms  (often  containing 
carbonate  of  lime)  of  varying  shapes 
and  bearing  fringe-like  tentacles  around 
+he  mouth.  1.  Bryozoans  form  tiny 
>ss-like  tufts  which  nearly  always 
ionize  and  suggest  the  Anthozoans  in 

itward  appearance,  though  they  are 
much  more  highly  organized.  With  few 
exceptions  the  Bryozoans  secrete  calca- 
^eous  Coral-like  skeletons.  2.  Brachi- 

~>ods  are  characterized  by  two  distinct, 

xternal  shells  (valves)  which  contain 
the  soft  portion  of  the  animal,  and  also 
a  pair  of  long,  spirally  coiled,  fringed  arms.  In  fossil  form  the 
Brachiopods  are  most  readily  distinguished  from  Certain  Mollusks 
(Pelecypods),  which  are  also  bivalves,  by  the  bilateral  symmetry  of 


Fig.  10 

Brachiopod  shells  (fossil 
forms).  The  lower  one 
shows  the  internal  spiral 
arms. 


Fig.  11 

A  modern  Pelecypod.  A,  side  view;  B,  end  view.  (After 
Howes,  from  Schuchert's  "Historical  Geology,"  permission 
of  John  Wiley  and  Sons.) 

the  shells.  That  is,  a  plane  of  symmetry  may  be  passed  through  the 
valves  at  right  angles  to  the  hinge  line.  Bryozoans  and  Brachi- 
opods are  both  very  abundant  as  fossils,  especially  in  the  older  rocks. 


20 


HISTORICAL  GEOLOGY 


VII.  MOLLUSKS,  like  Molluscoids,  lack  segmentation,  but  they 
are  more  highly  organized  with  more  or  less  distinctly  developed 
locomotive  organs  and  head.  Nearly  all  have  shells,  generally  ex- 
ternal, and  gills  for  respiration.  1.  Pelecypods  (e.g.  Oysters  and 
Clams)  are  always  supplied  with  a  pair  of  external  shells  nearly 
alike  and  hence  they  are  bivalves,  but  they  differ  from  the  Brachi- 

opods  (bivalves)  in  the 
absence  of  bilateral  sym- 
metry. The  head  is  less 
distinct  than  in  the  other 
Mollusks.  2.  Gastropods 
have  distinct  head  with 
eyes  and  one  or  two  pairs 
of  tentacles,  and  they  are 
almost  invariably  covered 
by  a  one-chambered  shell 
(e.g.  Snails).  3.  Cepha- 
lopods  have  well-defined 
foot;  head  armed  with 
tentacles;  and  large  com- 
plex eyes.  They  propel 
themselves  rapidly  by 
forcible  ejection  of  water. 
Tetrabranchs  (e.g.  modern 
Pearly  Nautilus)  are  the 
so-called  chambered  Ce- 


Foot 


Fig.  12 
and   B,   marine  forms; 


C,    phalopods    because    the 


Gastropods:    A 

land    Snail.      (From    Schuchert's    "His-    external  shell,  straight  or 
torical     Geology,"     permission     of     John 
Wiley  and  Sons.) 


coiled,    is    divided    into 
compartments.  They  are 
Dibranchs  (e.g.  so-called 


four-gilled  and  with  numerous  tentacles. 
Cuttle-fishes)  are  two-gilled;  with  either  eight  or  ten  tentacles; 
bag  for  secreting  an  inky  fluid;  and  almost  invariably  without 
external  shell.  Usually  there  is  a  sort  of  cigar-shaped  internal 
shell.  Mollusks  of  all  classes  have  been  abundantly  preserved  in 
rocks  of  all  but  the  earliest  geologic  ages. 

VIII.  ARTHROPODS  are  highly  characterized  by  longitudinal 
body  segmentation;  jointed  appendages  (usually  a  pair  from  each 
segment) ;  and  usually  by  a  pair  of  nerve  centres  in  each  segment. 
1.  Crustaceans  (e.g.  Lobsters  and  Crabs)  are  water  animals  breath- 


GENERAL  PRINCIPLES 


21 


ing  by  means  of  gills  or  through  the  body;  usually  with  two  pairs 
of  well-developed  antennae  (feelers) ;  and  covered  with  a  chitinous 
or  calcareous  crust  or  shell.  2.  Arachnids  (e.g.  Spiders  and  Scor- 
pions) are  land  Arthropods  breathing 
by  air-sacs;  have  four  pairs  of  legs; 
and  no  antennae.  3.  Myriapods  (e.g. 
Centipedes)  are  land  Arthropods  with 
numerous  legs;  one  pair  of  antennae; 
and  no  wings.  4.  Insects  (e.g.  Grass- 
hoppers and  Butterflies)  are  also  land 
Arthropods  with  one  pair  of  antennae, 
but  with  three  pairs  of  legs,  and  nearly 
always  with  wings. 

IX.  VERTEBRATES  are  eminently 
characterized  by  the  possession  of  a 
vertebral  column,  which,  in  all  but  the 
very  low  forms,  is  a  thoroughly  ossi- 
fied backbone.  Vertebrates  include  the  highest  known  of  all  ani- 
mals. 1.  Ostracoderms  (e.g.  Armour-fishes,  now  wholly  extinct) 
are  among  the  very  simplest  of  Vertebrates  (see  Fig.  80).  They 
are  of  particular  interest  from  the  standpoint  of  the  evolution  of 
the  Fishes  and  higher  Vertebrates.  Characteristic  features  will  be 


Fig.  13 

modern  chamber-shelled 
Cephalopod  (Nautilus)  show- 
ing the  internal  shell  struc- 
ture. 


Fig.  14 

A  modern  Squid.     (After  J.  H.  Blake,  from  Shimer's  "Introduction  to  the 
Study  of  Fossils,"  permission  of  The  Macmillan  Company.) 

given  beyond  in  connection  with  the  life  of  the  Devonian  period. 
2.  Fishes  always  live  in  water;  have  distinct  cartilaginous  or  bony 
vertebral  column;  distinct  jaws;  pairs  of  fins;  and  gills.  Sub- 
classes of  Fishes  will  be  described  later.  3.  Amphibians  (e.g.  Frogs 
and  Salamanders)  live  either  in  water  or  on  land.  In  the  early 
stage  of  development  of  the  individual  (e.g.  Tadpole  stage),  they 
are  aquatic,  and  breathe  by  gills,  while  in  the  adult  stage  they 
breathe  by  lungs  and  are  largely  terrestrial  in  habit.  They  never 


22  HISTORICAL  GEOLOGY 

have  fins.  4.  Reptiles  (e.g.  Snakes  and  Crocodiles),  though  in 
many  ways  like  Amphibians,  never  have  gills,  and  always  have 
scales  or  bony  plates  developed  from  the  skin.  They  are  the  most 
highly  organized  cold-blooded  animals.  5.  Birds  are  plainly  dis- 
tinguished from  all  other  animals  by  their  covering  of  feathers. 
They  are  too  familiar  to  need  special  description.  They  are  warm- 
blooded creatures  with  well-developed  heart  and  circulation  of 
blood.  6.  Mammals  (e.g.  Dog  and  Man)  include  the  highest  of 
all  organisms,  a  characteristic  being  that  they  all  suckle  the  young. 
They  are  mostly  quadrupeds,  covered  with  hair,  and  dwellers  on 
land.  The  Whale  is  an  exceptional  mammal. 

Vertebrate  fossils  are  common  and  of  special  interest  because 
they  show  the  development  of  the  higher  animals.  The  simplest 
(Ostracoderms)  have  been  found  in  rocks  of  Ordovician  age 
(see  below),  and  higher  and  higher  forms  were  gradually  intro- 
duced and  developed  until  the  most  complex  Mammals  appeared 
in  comparatively  recent  time. 


CHAPTER  II 

/ 

GENERAL    PRINCIPLES  —  C  ONCLUDED 

CORRELATION  OF  ROCK  FORMATIONS 

BY  Stratigraphy  is,,  .me.  ant  that  branch  of  geologic  science 
which  "arranges  the  roc&s  oHhe  earth's  crust  in  the  order  of  their 
appearance,  and  interprets  the  sequence  of  events  of  which  they 
form  the  records"  (A.  Geikie).  All  stratified  rocks  may  be  sub- 
divided into  formations  or  groups  of  strata,  each  of  which  is  marked 
either  by  a  characteristic  facies  or  assemblage  of  fossils,  or,  to 
greater  or  lesser  extents,  by  similarity  of  lithologic  features,  or 
by  both.  A  rock  formation  is  generally  considered  to  be  a  map- 
pable  unit,  that  is  its  area  can  be  delimited  upon  a  geologic  map. 
Subdivisions  of  formations  are  usually  called  members.  By  cor- 
jelation  of  formations  is  meant  the  determination  of  the  equiva- 
lon^i  nr  prnnfinp|  r>qi1iYn1Qnr.p|  r>f  rock  groups  or  tormatJons  jn 
^rirmg  ports  nf  f|iftj^irtV)jj  Exact  contemporaneity  for  widely 
separated  districts  cannot  be  expected  as  above  explained  in 
chapter  1.  In  general  the  criteria  of  correlation  may  be  divided 
into  two  classes,  namely,  geological  (physical)  and  paleontological 
(biological).1 

I.  GEOLOGICAL  (PHYSICAL)  CRITERIA.  In  many  cases  forma- 
tions carry  no  fossils  or  very^few,  and  it  is  then  necessary  to  seek 
means  of  correlation  without  their  aid.  None  of  the  geological 
(physical)  methods  can,  however,  be  applied  over  wide  areas  such 
as  opposite  sides  of  a  continent,  or  different  continents.  For  such 
wide  correlations,  criteria  derived  from  a  study  of  fossils  only  can 
be  used. 

1.  Continuity  of  deposit.  If,  as  shown  in  the  accompanying 
diagram  (Fig.  15),  continuity  can  be  traced  from  A  to  B,  it  is  quite 
certain  that  the  rock  masses  at  A  and  B  are  of  the  same,  or  very 
nearly  the  same,  age.  There  is  probably  no  more  important  means 
of  correlation  used  by  the  geologist  except  over  wide  areas. 

1  The  criteria  of  correlation  as  here  presented  are  based  largely  upon  uni- 
versity lectures  by  Dr.  W.  B.  Clark. 

23 


24 


HISTORICAL  GEOLOGY 


2.  Similarity  of  materials.  Rock  formations  not  actually 
continuous,  though  not  too  widely  separated,  are  often  correlated 
by  noting  similarity  or  identity  of  lithologic  character,  especially 

if  there  are  any  locally  peculiar 
features.  Older  geologists  were 
inclined  to  overwork  this  method 
of  correlation  by  applying  it  over 
areas  of  too  great  extent,  in 
some  cases  even  suggesting  iden- 
tity of  age  of  deposits  on  oppo- 
site sides  of  the  ocean  by  this 
means.  The  danger  of  'such 
application  is  apparent  when  we 
realize  that,  for  example,  a  sand- 
stone of  very  early  (Cambrian) 
age  may  be  exactly  like  sand- 
stone of  much  later  (Tertiary) 
of  age. 

^*-  3.  Similarity  of  sequence.  A 
succession  of  strata  4n4wo  places 
like  A  and  B  (Fig.  16),  and  not  continuous  on  the  surface,  may 
be  correlated  on  the  basis  of  similarity  of  sequence,  particularly 
when  each  formation  at  one  place 
(A)  shows  little  or  no  difference 
in  lithologic  character  or  thick- 
ness as  compared  with  ea,ch 
formation  at  the  othep  place  (B)*, 
4.  Similarity  of  degree  of 
change,  or  structural  relations.  By 
finding  similarly  changed  or 
metamorphosed  rocks  in  the 
same  vicinity,  they  may  thus  be 
correlated.  For  instance,  in  the 
accompanying  diagram  (Fig.  17)  Diagram  to  mustrate  corre,ation  of 

rock  formations  by  similarity  of 


Fig.  15 

Diagram  to  illustrate  correlation 
rock  formations  by  continuity 
deposit.  (W.  J.  M.) 


I.  I.I.I 


B 


Fig.  16 


sequence.     (W.  J.  M.) 


it  is  evident  that  the  rocks  of 

group  A  are  older  than  those  of 

group  B,  and  these  in  turn  older 

than  C.    Outcrops  over  limited  areas  at  least  can  thus  be  placed  in 

one  of  these  three  groups.     By  way  of  illustration,  the  (pre-Pale- 

ozoic)  rocks  of  the  Highlands  of  the  Hudson  in  southeastern  New 


GENERAL  PRINCIPLES  —  CONCLUDED 


25 


York  are  highly  metamorphosed  and  folded,  with  indurated,  folded 
(Ordovician)  strata  resting  upon  their  north  side,  and  indurated, 
non-folded,  and  slightly  tilted  (Triassic)  strata  coming  against 
them  on  the  south  side.  Each  of  these  groups  of  rocks  represents 
a  distinctly  different  geologic  age.  This  method  cannot  be  used 
over  wide  areas  such  as  different  parts  of  a  continent,  because  for 
instance,  certain  strata  (Cretaceous)  in  the  eastern  part  of  the 
United  States  may  be  unconsolidated  and  horizontal,  while  rocks 
of  the  same  age  are  highly  folded  in  the  western  United  States. 
5.  Study  of  adjacent  lands.  Examination  of  the  materials  of 


Fig.  17 

Diagram  to  Illustrate  correlation  of  rock  formations  by 
degree  of  change  or  structure.     (W.  J.  M.) 

the  Coastal  Plain  of  our  Atlantic  sea-board  clearly  shows  them  to 
have  been  largely  derived  from  the  rocks  of  the  Piedmont  Plateau 
and  Appalachians,  and  hence  these  Coastal  Plain  materials  are 
the  younger.  Also  the  peneplain  character  of  the  surface  of  the 
Piedmont  Plateau  proves  the  greater  age  of  this  region  because  the 
peneplain  was  being  produced  by  wearing  off  the  very  materials 
which  were  deposited  in  the  adjacent  ocean  to  produce  what  are 
now  called  the  Coastal  Plain  deposits. 

6.  By  diastrophism.  According  to  Chamberlin,1  the  great 
deformations  of  the  earth's  crust  have  been  of  periodic  occurrence. 
Each  great  movement  has  "tended  toward  the  rejuvenation  qf 
the  continents  and  toward  the  firmer  establishment  of  the  great 
(oceanic)  basins."  Between  any  two  great  diastrophic  movements 
there  has  been  a  time  of  quiescence  when  the  base-leveling 
processes  have  more  or  less  lowered  the  continents.  Such  "base- 
leveling  of  the  land  means  contemporaneous  filling  of  the  sea 

1  T.  C.  Chamberlin:    Diastrophism  the  Ultimate  Basis  of  Correlation,  in 
Jour.  GeoL,  Vol.  17,  1909,  pp.  685-693. 


26  HISTORICAL  GEOLOGY 

toWA,  p&^+*r**'     ejfc. 

basins  by  transferred  matter"  with  resultant  encroachment  of 
the   sea  over  the  land  "essentially  contemporaneous  the  world 
over/'  which  in  turn  implies  "a  homologous  series  of  deposits  the 
^      world  over."     Thus  the  times  of  great  diastrophism  (recognized 
(^***&>y  great  unconformities  and  overlapping  deposits)  should  form  the 
)c*jj)      basis  of  correlating  at  least  the  larger  groups,  or  even  systems,  oL 
strata  in  the  earth's  crust.  -^Cut^u^  d  fidLA.  ~ 

II.  PALEONTOLOGICAL  (BIOLOGICAL)  CRITERIA.  The  signifi- 
cance of  fossils  in  the  determination  of  geological  chronology  has 
already  been  discussed,  but  it  should  here  be  repeated  for  emphasis 
that  "order  of  superposition"  of  the  strata,  studied  in  connection 
with  their  fossil  content,  furnishes  the  general  standard  for  building 
up  a  geological  chronology,  and  affords  the  best  basis  for  the  cor- 
relation of  formations.  In  fact,  for  correlation  of  formations  in 
distant  portions  of  a  continent,  or  different  continents,  paleonto- 
logical  criteria  alone  are  satisfactory. 

1.  Identity  of  species.     This  is  an  extremely  important  method 
of  correlation,  especially  when  species  with  wide  geographic  dis- 
tribution and  short  geologic  range  are  employed.     It  is  not  wise 
to  depend  upon  a  single  species  for  the  correlation  of  far  distant 
formations,  because  then  the  time  necessary  for  the  migration  of 
the  species  must  be  considered.     This  seldom  gives  trouble  be- 
cause the  geologist  usually  deals  with  a  number  of  rapid-moving 
species.     In  a  restricted  area,  where  formations  are  to  be  correlated, 
the  same  organisms  may  have  continued  for  a  long  time,  but  near]^ 
always  some  peculiar  species  furnishes  the  clew. 

2.  Aggregations  of  forms.     When  groups  of  strata  in  different 
areas  carry  similar  aggregations  of  similar  forms,  the  groups  of 
strata  may  be  safely  correlated.     Even  though  a  small  percentage 
of  the  species  vary,  the  method  still  holds  because  such  varia- 
tions are  to  be  expected  on  account  of  migratory  and  geographic 
conditions. 

3.  Stage  in  the  evolution  of  organisms.     Since  there  has  been  a 
gradual  development  of  life  with  increasing  complexity  throughout 
geologic  time,  the  stage  of  development  or  evolution  shown  by  the 
fossils  in  a  group  of  strata  will  serve  as  a  basis  for  general  correla- 
tion at  least.     Each  era,  or  even  period,  shows  a  characteristic 
stage  of  evolution  of  forms. 

*3  4.    Percentage  of  living  species.     This  applies  only  to  rock  for- 
mations of  later  geologic  time,  because  the  older  rocks  contain  no 


GENERAL  PRINCIPLES  —  CONCLUDED 


27 


species  like  those  now  living.  The  percentage  of  living  species 
becomes  greater  and  greater  as  the  present  is  approached,  and  on 
this  basis  Lyell  sub-divided  a  late  period  (Tertiary)  into  three 
epochs. 

In  any  correlation  problem  the  geologist  strives  to  use  as  many 
of  the  above  criteria  as  possible,  the  certainty  of  the  correlation 
being  more  firmly  established  when  several  geological  and  paleon- 
tological  criteria  are  used  together. 


SIGNIFICANCE  OF  UNCONFORMITIES 

Thus  far  our  discussion  has  been  based  largely  upon  the  assump- 
tion of  conformable  strata,  but  many  times  the  succession  of  strata 
(so-called  " section")  under  study  shows  one  or  more  unconfor- 
mities. Since  an  unconformity  represents  a  time  of  erosion,  or 
possibly  a  time  of  non-deposition  of 
sediments,  it  is  obvious  that  it  sig- 
nifies an  absence  of  both  the  strata 
and  life  records  for  a  greater  or 
lesser  length  of  time*  The  missing 
records  for  a  given  region  can,  how- 
ever, generally  be  found  by  going 
to  some  other  locality  where  deposi- 
tion of  sediments  was  not  inter- 
rupted at  the  time  when  the  uncon- 
formity was  being  produced. 

Without  the  aid  of  fossils,  in  the 
ordinary  case  of  unconformity,  we 
could  tell  that  the  land  emerged 
above  water,  was  eroded,  and  again 
submerged,  but  we  could  not  tell  how  much  time  the  erosion 
interval  involved  (Fig.  18).  But  by  noting  the  fossils  in  the 
youngest  strata  just  below  the  eroded  surface,  and  in  the  oldest 
strata  just  above  it,  we  could  tell  what  epochs  or  periods  are 
represented  by  the  erosion  interval  by  a  comparison  with*  the 
standard  geologic  section  of  the  world  (see  table  near  the  c\ose  of 
this  chapter). 

Because  the  fossils  immediately  above  and  below  the  line  of  a 
profound  unconformity  show  such  marked  differences,  the  earlier 
geologists  were  misled  into  thinking  that  each  great  unconformity 


Fig.  18 

Diagram  to  illustrate  the  sig- 
nificance of  unconformities. 
The  lower  strata  (A)  were 
folded,  raised  above  water, 
eroded  and  then  submerged, 
after  which  the  upper  strata 
(B)  were  deposited  and  then 
tilted.  (W.  J.  M.) 


28  HISTORICAL  GEOLOGY 

signified  an  awful  catastrophe  (physical  and  organic)  which  devas- 
tated the  earth  and  destroyed  all  organisms,  after  which  came  a 
period  of  tranquillity  when  a  new  set  of  organisms  was  created. 
This  has  been  called  the  doctrine  of  catastrophism.  In  opposition 
to  this  view  Sir  C.  Lyell  promulgated  the  doctrine  of  uniformita- 
rianism  which  holds  that  the  evolution  of  the  earth  and  its  in- 
habitants has  progressed  practically  uniformly,  and  that  missing 
records  in  one  place  are  to  be  found  in  other  places.  Today 
Lyell's  view  is  generally  accepted  with  the  modification  that  times 
of  comparatively  more  rapid  earth  disturbance,  and  probably 
changes  in  organisms,  have  occurred. 


TRANGRESSIONS  AND  RETROGRESSIONS  OF  THE  SEA 

During  our  study  of  the  clearly  recorded  portion  of  the  earth's 
history  we  shall  find  positive  evidence  of  repeated  transgressions 
and  retrogressions  of  marine  waters  over  various  portions  of  what 
are  now  the  continental  areas.  Since  subsidences  or  elevations 
of  the  lands  are  not  the  only  known  causes  of  sea  transgressions 
and  retrogressions,  we  shall,  in  the  following  pages,  refer  to  sub- 
mergences and  emergences  of  the  lands  unless  there  is  good  evi- 
dence for  more  specific  statement  in  any  case. 

Submergence  may  be  caused  either  by  (1)  sinking  of  the  land; 
(2)  rise  of  the  sea;  or  (3)  both  together.  "Both  the  lowering  of 
the  land  and  the  rise  of  the  sea  may  be  due  to  gradation,  to  dias- 
trophism,  or  to  the  two  combined.  Gradation  is  perpetual  and 
inevitable  where  land  and  sea  exist.  ...  It  has  been  computed  that 
if  the  earth,  in  its  present  condition,  were  to  remain  without  defor- 
mation long  enough  for  the  continents  to  be  base-leveled,  the 
deposition  of  the  sediments  thus  derived  in  the  sea  would  raise  the 
sea-level  about  650  feet.  This  would  submerge  a  large  part  of 
the  base-leveled  land.  .  .  .  Base-leveling  implies  a  nearly  undis- 
turbed attitude  of  the  land  and  sea,  and  hence  in  itself  favors  the 
view  that  no  great  deformation  affected  the  continent  while  it,  was 
going  on."  1  Much  submergence  of  lowlands  would  take  place 
long  before  such  wide-spread  base-leveling  had  been  accomplished. 
Sinking  of  the  land  (see  below)  would  of  course  cause  submergence, 
but  whether  submergence  of  the  land,  in  any  given  case,  has  been 

1  Chamberlin  and  Salisbury:   College  Geology,  p.  479. 


GENERAL  PRINCIPLES  —  CONCLUDED  29 

due  only  or  largely  to  sinking  or  gradation  or  to  both  is  at  present 
often  difficult  or  impossible  to  determine,  though  it  is  quite  certain 
that  both  processes  have  often  been  operative. 

Emergence  may  be  caused  either  by  (1)  rise  of  the  land;  (2) 
lowering  of  the  sea;  or  (3)  both  combined.  Except  rather  locally 
as  in  the  cases  of  mountain-making  (orogenic)  movements,  it  seems 
doubtful  if  there  is  any  good  evidence  for  very  considerable  actual 
uplifts  of  extensive  land  areas  thus  causing  great  sea  retrogressions. 
On  the  other  hand,  the  earth  is  certainly  a  contracting  body  with 
its  whole  surface  approaching  nearer  and  nearer  to  its  centre.  It 
appears  that  "the  rigidity  of  the  earth  may  be  such  that  its  outer 
parts  are  able  to  withstand  for  a  time  the  strain  set  up  by  contrac- 
tion. As  the  strain  accumulates,  it  ultimately  overcomes  the  resis- 
tance, and  the  outer  part  of  the  earth  yields.  If  the  yielding  results 
in  the  sinking  of  the  ocean  basin,  the  surface  of  the  water  is  drawn 
down,  and  the  surrounding  lands  seem  to  rise,  unless  they  sink  as 
much  as  the  surface  of  the  sea  does  at  the  same  time.  The  lowering 
of  the  sea  surface,  because  of  the  sinking  of  the  sea-bottom,  is  prob- 
ably the  most  fundamental  single  cause  of  the  apparent  rise  of 
the  land.  The  periodic  emergences  of  the  continents,  alternating 
with  periodic  submergences  in  the  course  of  geological  history,  are 
perhaps  to  be  thus  explained.  Periodic  submergences,  on  the  other 
hand,  might  be  explained  by  the  sinking  of  the  continental  segments 
of  the  earth,  or  by  such  sinking  combined  with  the  processes  already 
referred  to  which  cause  the  rise  of  the  sea."  l 


PALEOGEOGRAPHY 

Paleogeography  literally  means  "ancient  geography"  and  deals 
with  the  geographic  conditions  of  the  earth  during  geologic  time. 
In  making  a  paleogeographic  map  to  represent  North  America  at 
a  given  time  in  its  history,  the  attempt  is  made  to  show  the  rela- 
tions of  lands  and  waters  with  distinctions  between  deep  and 
epicontinental  seas  where  possible,  areas  of  continental  deposition, 
directions  of  ocean  currents,  etc.  Until  quite  recent  years  there 
were  only  crude  attempts  at  making  such  maps  for  North  America, 
for  the  knowledge  of  the  continent  was  not  sufficient  to  form  a 

1  R.  D.  Salisbury:  Physiography,  Advanced  Course,  pp.  401-402. 


30  HISTORICAL  GEOLOGY 

reasonable  basis  upon  which  to  work.  Within  the  last  few  years, 
however,  several  sets  of  paleogeographic  maps,  notably  those  by 
Bailey  Willis  l  and  Charles  Schuchert,2  have  been  prepared.  The 
Willis  maps  are  used  in  this  text,  but  the  student  will  do  well  to 
compare  the  Schuchert  maps  with  these  as  the  different  periods  are 
taken  up. 

Willis  gives  a  general  statement  of  the  lines  of  evidence  used 
in  the  construction  of  his  maps  as  follows :  "  A  certain  period  having 
been  selected  as  that  which  should  be  mapped,  the  epicontinental 
strata  pertaining  to  that  time  interval  have  been  delineated.  The 
phenomena  of  sedimentation  and  erosion  have  then  been  correlated, 
with  a  view  to  determining  the  sources  of  sediment  and  topographic 
conditions  of  land  areas,  and  from  these  data  the  probable  positions 
of  lands  have  been  more  or  less  definitely  inferred.  Thus,  certain 
areas  within  the  continental  margin  are  distinguished  as  land  or  sea, 
and  these  areas  may  be  defined  as  separate  bodies  or  connected 
according  to  inferences  based  upon  isolated  occurrences  or  upon 
later  effects  of  erosion.  It  is  assumed  that  the  great  oceanic  basins 
and  such  deeps  as  the  Gulf  of  Mexico  and  Caribbean  have  been 
permanent  features  of  the  earth's  surface  at  least  since  some  time 
in  the  pre-Cambrian  .  .  . 

"From  the  geographic  conditions  thus  developed,  inferences 
regarding  the  climate  and  the  life  habitats  of  the  time  may  be 
drawn.  If  now  we  turn  to  the  records  of  paleontology,  and  com- 
pare the  distribution  of  faunas  and  floras3  with  the  conditions 
of  distribution  which  should  result  from  the  inferred  physical 
phenomena,  we  may  check  the  whole  line  of  reasoning  and 
by  a  readjustment  draw  a  step  nearer  to  the  truth.  This  is  the 
method  which  has  been  pursued  in  making  the  maps  of  North 
America."  4 

It  should  be  borne  in  mind  that  such  paleogeographic  maps 
are  generalized  and  rather  tentative  as  regards  many  details  — 
generalized  because  each  map  represents  a  considerable  time  period 
so  that  certain  more  local  geographic  changes  during  the  period 

1  B.  Willis:  Jour.  Geol,  Vol.  17,  1909. 

2  C.  Schuchert:  Bull  Geol.  Soc.  America,  Vol.  20,  1910. 

3  The  term  "fauna"  refers  to  an  assemblage  of  animals  populating  a 
given  area  during  a  certain  epoch.     In  a  similar  sense  the  term  "flora"  is 
applied  to  an  assemblage  of  plants. 

4  B.  Willis:  Jour.  Geol.,  Vol.  17,  1909,  pp.  201-202. 


GENERAL  PRINCIPLES  —  CONCLUDED  31 

are  not  indicated,  and  tentative  because  of  lack  of  knowledge 
concerning  many  areas  and  lack  of  certainty  in  the  correlation  of 
formations  in  certain  other  areas.  With  progress  in  knowledge 
of  the  strata,  less  generalized  and  more  accurate  maps  will  be  made. 
Nevertheless  the  series  of  maps  used  in  this  text  will  serve  to  give 
the  beginner  a  very  good  idea  of  the  broader  features  in  the  geo- 
graphic development  of  our  continent. 


CLASSIFICATION  OF  GEOLOGIC  TIME 

We  have  already  shown  how,  by  employing  the  law  of  super- 
position of  the  strata  together  with  the  law  of  included  fossils, 
the  rock  formations  of  various  parts  of  the  earth  may  be  corre- 
lated and  built  up  according  to  their  natural  order  of .  age  into  a 
standard  for  comparison  or  a  geologic  column.  The  subdivisions 
of  the  geologic  column  represent  the  times  when  the  successive 
rock  formations  were  deposited.  Different  names  have,  from 
time  to  time,  been  assigned  to  these  divisions  which  are  in  more 
or  less  general  use. 

For  a  long  time  the  subdivisions  of  the  geologic  column  were 
made  almost  solely  on  the  basis  of  marked  differences  in  fossils, 
but  it  is  now  recognized  that  such  differences  were,  in  no  small 
degree,  caused  by  corresponding  changes  in  the  environment  in 
which  the  organisms  lived,  or,  in  other  words,  by  changes  in  the 
climate,  the  topography,  the  relations  of  land  and  sea,  etc.  So  we 
now  try  to  divide  the  geologic  record  at  the  points  where  the 
revolutionary  physical  changes  are  indicated,  and  to  make  cor- 
responding divisions  of  geologic  time  itself.  Thus  there  are  two 
kinds  of  divisions  —  one  for  the  rocks  themselves,  and  the  other 
for  the  time  represented  by  the  rocks. 

The  following  time  and  rock  scales  have  been  adopted  by  the 
International  Geological  Congress.  Immediately  following  these 
scales  is  given  in  descending  the  table  of  main  geological  divisions 
as  now  recognized  in  North  America. 

Time  scale  Rock  scale 

Era Group 

Period System 

Epoch Series 

Age Stage 


32  HISTORICAL  GEOLOGY 

TABLE  OF  MAIN  GEOLOGICAL  DIVISIONS 
Era  and  group       Period  and  system 

CENOZOIC        (Quaternary. 
\  Tertiary. 

f  Cretaceous. 
MESOZOIC       {  Jurassic. 
[  Triassic. 

Permian. 

Pennsylvanian  (Upper  Carboniferous). 
Mississippian  (Lower  Carboniferous). 
PALEOZOIC     {  Devonian. 
Silurian. 
Ordovician. 
%  Cambrian. 

PROTEROZOIC  {  Algonkian. 
ARCHEOZOIC    {  Archean. 

The  names  of  eras  follow  a  definite  plan  depending  upon  the 
great  life  stages.  Thus  Archeozoic  means  literally  "primitive  or 
beginning  life";  Proterozoic  means  " earlier  or  less  primitive 
life";  Paleozoic  means  "ancient,  life";  Mesozoic  means  "inter- 
mediate life;"  and  Cenozoic  means  "recent  life."  The  period 
names  do  not  follow  such  a  definite  plan  of  nomenclature, 
various  ideas  being  represented.  These  names  will  be  explained 
when  the  different  periods  are  taken  up  for  discussion. 

COMPARISON  OF  HUMAN  AND  GEOLOGIC  HISTORY 

One  of  the  most  striking  differences  between  human  and  geo- 
logic history  is  the  extreme  brevity  of  the  one  as  compared  with 
the  vast  time  represented  by  the  other.  Human  history  is  to  be 
measured  by  some  thousands  of  years,  while  geologic  history  must 
be  measured  by  at  least  tens  of  millions  of  years.  A  recent  event, 
geologically  speaking,  like  that  of  the  building  of  the  Coast  Range 
Mountains,  or  the  carving  out  of  a  tremendous  canyon  like  the 
Grand  Canyon  of  the  Colorado  in  Arizona,  required  some  hundreds 
of  thousands,  if  not  a  few  millions,  of  years.  Human  history  is 
roughly  divided  into  certain  ages  according  to  the  predominant 
influence  of  some  person,  nation,  principle,  or  force.  Thus  we 
speak  of  the  "Age  of  Pericles,"  the  "Roman  Period,"  the  "Age 
of  the  French  Revolution,"  or  the  "Age  of  Electricity."  Geologic 


GENERAL  PRINCIPLES  —  CONCLUDED  33 

history  is  sub-divided  according  to  great  predominant  physical  or 
organic  phenomena  as,  for  example,  the "  Appalachian  Revolution" 
(toward  the  close  of  the  Paleozoic  era),  the  " Rocky  Mountain 
Revolution"  (toward  the  close  of  the  Mesozoic  era),  the  "Age  of 
Fishes"  (Devonian  period),  the  "Age  of  Mammals"  (Cenozoic  era). 
Students  of  earth  history,  like  students  of  human  history,  must 
be  very  careful  to  make  a  distinction  between  events  and  records 
of  events,  because  by  no  means  all  historical  events  are  recorded. 
Events  are  continuous,  while  their  records  are  usually  much  inter- 
rupted and  apparently  sharply  separated  from  each  other.  In  both 
geologic  and  human  history,  times  or  periods  of  comparatively 
quiet  and  slow  change  have  often  given  way  to  times  of  compara- 
tively rapid,  to  even  revolutionary,  change. 

SELECTED    GENERAL  REFERENCES 

WILLIS:  Index  to  the  Stratigraphy  of  North  America,  Accompanied  by  a  Geo- 
logic Map  of  North  America.  Prof.  Paper  71,  U.  S.  Geol.  Survey.  A 
very  comprehensive  work  with  many  references  and  quotations. 

CHAMBERLIN  AND  SALISBURY:  Geology,  Vols.  2  and  3  (Henry  Holt  Co.,  1906). 
A  very  elaborate  recent  American  work. 

CHAMBERLIN  AND  SALISBURY:  College  Geology,  Part  2  (Henry  Holt  Co.,  1909). 
A  briefer  discussion  than  in  the  larger  work  of  these  authors. 

DANA:  Manual  of  Geology,  Part  4  (American  Book.  Co.,  1895).  A  very  elabo- 
rate older  American  work. 

GEIKIE:  Text-book  of  Geology,  Vol.  2  (Macmillan  Co.,  1903).  A  comprehensive 
.  English  work  with  emphasis  upon  European  geology. 

KAYSER:  Lehrbuch  der  Geologie,  Part  2  (F.  Enke,  Stuttgart,  1912).  A  com- 
prehensive German  work  with  emphasis  upon  European  geology. 

HAUG:  Traite  de  Geologie,  Vol.  2  (A.  Colin,  Paris,  1911).  A  comprehensive 
French  work  with  emphasis  upon  European  geology. 

WILLIS  AND  SALISBURY:  Outlines  of  Geologic  History  with  Especial  Reference 
to  North  America  (University  of  Chicago  Press,  1910).  Not  a  text-book, 
but  contains  important  general  papers  by  various  American  geologists. 

BLACKWELDER:  Regional  Geology  of  the  United  States  of  North  America  (Stechert 
&  Co.,  1912).  Contains  brief  outlines  of  the  stratigraphy  and  geologic 
history  of  the  United  States. 

LE  CONTE:  Elements  of  Geology,  Part  3  (Appleton  and  Co.)  An  older  fairly 
comprehensive  treatment  of  historical  geology  with  special  reference  to 
North  America. 

SCOTT:  An  Introduction  to  Geology,  Part  4  (Macmillan  Co.,  1907).  A  fairly 
comprehensive  discussion  of  earth  history. 

PIRSSON  AND  SCHUCHERT:  Text-book  of  Geology,  Part  2  (John  Wiley  &  Sons, 
1915).  A  fairly  comprehensive  treatment  of  historical  geology. 

CLELAND:  Geology,  Physical  and  Historical,  Part  2  (American  Book  Co., 
1916).  A  fairly  comprehensive  treatment  of  historical  geology. 


34  HISTORICAL  GEOLOGY 

BLACKWELDER  AND  BARROWS:  Elements  of  Geology,  Part  2  (American  Book 
Co.,  1911).  An  elementary  discussion  of  historical  geology. 

NORTON:  Elements  of  Geology,  Part  3  (Ginn  and  Co.,  1905).  A  very  elemen- 
tary discussion  of  historical  geology. 

TARR:  Elementary  Geology,  Part  3  (Macmillan  Co.,  1897).  A  very  brief  dis- 
cussion of  earth  history. 

BRIGHAM:  A  Text-book  of  Geology  (Appleton  and  Co.,  1902).  Contains  a  brief 
treatment  of  historical  geology. 

DANA:  Text-book  of  Geology,  Part  4  (American  Book  Co.,  1897).  A  brief  dis- 
cussion of  earth  history. 

GRABAU:  The  Principles  of  Stratigraphy  (A.  G.  Seiler  and  Co.,  1913).  An 
elaborate  account  of  stratified  rocks  and  their  significance. 

SHIMER:  An  Introduction  to  the  Study  of  Fossils  (Macmillan  Co.,  1914).  An 
elementary  treatment  of  the  subject  of  paleontology. 

ZITTEL-EASTMAN:  Text-book  of  Paleontology,  2  Vols.  (Macmillan  Co.,  1913). 
An  elaborate  treatment  of  the  subject  of  paleontology. 

WOODS:  Paleontology  (Cambridge  University  Press,  1902).  A  brief  discus- 
sion of  invertebrate  paleontology. 

JORDAN  AND  KELLOGG:  Evolution  and  Animal  Life  (Appleton  and  Co.,  1907). 
Organic  evolution  discussed  in  an  easily  understood  manner. 

MOULTON:  Introduction  to  Astronomy,  Chapter  15  (Macmillan  Co.,  1906). 
A  brief  discussion  of  the  evolution  of  the  Solar  System.  ^ 

Certain  of  the  larger  works  above  named,  especially  Willis' 
"Index  to  the  Stratigraphy  of  North  America/'  Chamberlin  and 
Salisbury's  "Geology,"  and  Geikie's  "Text-book  of  Geology," 
are  very  rich  in  important  references  to  the  literature  dealing  with 
historical  geology. 


CHAPTER   III 
ORIGIN    AND    PRE-GEOLOGIC    HISTORY    OF    THE    EARTH 

IF  we  define  geology  as  the  study  of  the  history  of  the  earth 
and  its  inhabitants  as  revealed  in  the  rocks,  it  is  evident  that  the 
problems  of  the  origin  and  very  early  development  of  the  earth  are 
strictly  astronomic  rather  than  geologic.  It  is  generally  agreed 
that  geological  history  did  not  begin  till  the  ordinary  earth  proc- 
esses, such  as  weathering  and  erosion,  transportation  and  depo- 
sition of  sediments,  etc.,  began  to  operate.  Since,  however,  the 
pre-geologic  condition  of  the  earth  must  have  gradually  given  way 
to  its  geologic  condition,  it  is  a  matter  of  interest  for  the  geologist 
to  consider  the  hypotheses  regarding  the  very  early  development 
of  the  earth. 

THE  SOLAE  SYSTEM 

The  sun  has  a  diameter  of  about  866,000  miles,  and  a  volume 
1,300,000  times  that  of  the  earth.  Around  this  central  sun  eight 
planets  —  Mercury,  Venus,  Earth,  Mars,  Jupiter,  Saturn,  Uranus, 
and  Neptune  —  revolve  in  nearly  circular  orbits.  Three  of  these 
planets  —  Mercury,  Venus,  and  Mars  —  are  smaller  than  the  earth, 
while  the  others  are  larger,  Jupiter  being  1,300  times  as  large. 
The  earth  is  about  93,000,000  miles  from  the  sun  and  requires  one 
year  for  a  trip  in  its  orbit  around  the  sun,  while  Neptune,  the  most 
distant  planet,  is  about  2,800,000,000  miles  from  the  sun  and  re- 
quires 164  years  for  a  revolution  about  the  sun.  Each  planet  also 
rotates  upon  its  axis,  the  earth  accomplishing  a  rotation  every 
twenty-four  hours.  Most  of  the  planets  have  smaller  bodies  called 
satellites  or  moons  revolving  about  them,  such  as  Earth  with  its 
one  moon,  Saturn  with  eight  moons,  etc.  The  sun  and  the  eight 
planets  with  their  satellites,  together  with  a  group  of  many  small 
independently  revolving  bodies  called  "planetoids,"  comprise  the 
solar  system.  That  this  solar  system  constitutes  only  a  very  small 
part  of  the  universe  is  clearly  proved  by  the  fact  that  the  nearest 
fixed  star  is  several  trillions  of  miles  from  the  earth. 

35 


36  HISTORICAL  GEOLOGY 

Some  of  the  well-known  facts  which  any  hypothesis  of  the 
origin  of  the  solar  system  must  explain  are  as  follows:  (1)  The 
planet  orbits  are  all  elliptical,  but  nearly  circular;  (2)  the  orbits 
lie  in  nearly  the  same  plane;  (3)  all  planets  revolve  about  the  sun 
in  the  same  direction;  (4)  the  sun's  direction  of  rotation  is  the  same 
as  that  of  the  planets'  revolution;  (5)  the  planes  of  the  planets' 
rotation  nearly  coincide  with  the  planes  of  their  orbits  (except 
Uranus  and  Neptune);  (6)  the  direction  of  the  planets'  rotation 
is  the  same  as  that  of  their  revolution;  and  (7)  the  satellites  re- 
volve in  the  direction  of  rotation  of  their  planets  (two  or  three 
exceptions) . 

HYPOTHESES  OF  EARTH  ORIGIN 

Nebular  or  Ring  Hypothesis.  —  In  1796  Laplace  published  a 
remarkable  work  on  astronomy,  and  in  its  last  chapter  he  put  forth 
his  now  well-known  hypothesis  regarding  the  origin  of  the  solar 
system.  He  postulated  a  spheroidal  mass  of  very  highly  heated, 
incandescent  gas  or  nebula  greater  in  diameter  than  the  present 
solar  system,  this  whole  mass  rotating  in  the  direction  of  the  revolu- 
tion of  the  existing  planets.  Due  to  loss  of  heat  by  radiation,  this 
mass  contracted  and  its  shrinkage  necessarily  made  it  rotate  more 
rapidly  upon  its  axis,  at  the  same  time  causing  the  centrifugal  force 
on  its  outside  to  become  stronger  and  stronger.  Finally  the  centrif- 
ugal force  at  the  equator  became  equal  to  the  force  of  gravity  and 
the  equatorial  portion  was  left  off  (not  thrown  off)  as  a  ring  sur- 
rounding the  contracting  remainder.  The  materials  of  the  ring 
condensed  to  form  the  outermost  planet.  By  continued  contrac- 
tion of  the  rotating  nebula,  the  other  rings  and  planets  were  formed. 
The  satellites  were  produced  in  a  similar  manner  by  rings  left  off 
by  the  shrinking  planets. 

Briefly,  according  to  this  hypothesis,  the  earth  was  originally 
highly  heated  and  much  larger  than  now.  During  its  cooling  and 
contraction,  its  original  hot  and  dense  atmosphere,  which  contained 
all  the  earth's  water  in  the  form  of  vapor,  gradually  became  thinner 
due  to  absorption  by  the  earth.  When  the  conditions  of  pressure 
and  temperature  were  favorable,  water  vapor  condensed  to  form 
the  hydrosphere.  The  oldest  rocks  must  have  been  igneous,  that 
is  they  were  portions  of  the  original  crust  formed  by  cooling  of  the 
molten  globe. 

For  over  a  hundred  years  the  Laplacian  hypothesis  has  exerted 


ORIGIN  OF  THE  EARTH 


37 


a  profound  influence  upon  science,  philosophy,  and  theology,  and 
certainly  many  of  the  important  phenomena  of  the  solar  system 
are  explained  by  it.  Some  serious  objections  to  it  may,  however, 
be  briefly  stated  as  follows:  (1)  Nearly  all  existing  nebulas  are 
spiral  and  not  circular;  (2)  spectroscopic  study  shows  that  these 
nebulas  do  not  consist  of  gas,  but  rather  of  discrete  liquid  or  solid 
particles;  (3)  the  backward  revolutions  of  certain  satellites  oppose 
the  hypothesis;  (4)  rings  could  not  have  been  left  off,  that  is  there 
could  have  been  no  intermit- 
tent process  of  the  sort;  and 
(5)  it  is  not  at  all  clear  how 
the  matter  of  the  rings  could 
have  condensed  into  planets. 
Planetesimal  or  Spiral 
Hypothesis. — It  is  a  remark- 
able fact  that,  although  many 
thousands  of  nebulas  are 
known,  there  are  very  few 
examples  of  ring  nebulas  of 
the  Laplacian  type  among 
them.  Spiral  forms  are 
very  common,  especially  the 
smaller  ones.  Also,  as  above 
stated,  spectroscopic  study  of  Fig.  19 

these  nebulas  shows  them  to        A  very   symmetrical   spiral   nebula  in 

be  made  up  of  discrete  (liquid          ^sces   <M-   74>;_  phot°  *y  Lick 
Vjx          ,.  ,  ,,  Observatory.        (From    Chamberlin 

or  solid)  particles  rather  than  and  Salisbury>s  "Geology,"  permis- 
of  gas.  ^  The  Planetesimal  sion  of  Henry  Holt  and  Company.) 

hypothesis,1    formulated    by 

Chamberlin  and  Moulton,  "postulates  that  the  matter  of  which 
the  sun  and  the  planets  are  composed  was,  at  a  previous  stage  of 
its  evolution,  in  the  form  of  a  great  spiral  swarm  of  discrete  par- 
ticles whose  positions  and  motions  were  dependent  upon  their 
mutual  gravitation  and  their  velocities"  (Moulton).  A  nebula 
of  this  sort  comprised  a  luminous  central  mass  (the  future  sun) 
from  the  opposite  sides  of  which  two  luminous  spiral  arms  streamed 
out  with  occasional  larger  masses  or  knots  along  each  arm,  and  with 
dark  lanes  between  the  arms  (see  Fig.  19).  Also  some  nebulous 

1  An  elaborate  discussion  of  this  hypothesis  may  be  found  in  Chamberlin 
and  Salisbury's  Geology,  Vol.  2. 


38 


HISTORICAL  GEOLOGY 


matter  occupied  the  spaces  between  the  arms.  Such  a  distribution 
of  matter  in  a  spiral  shows  that  the  form  could  not  have  been 
maintained  by  gaseous  pressure,  as  in  the  Laplacian  hypothesis, 
but  rather  by  the  movements  of  the  separate  particles  or  masses. 
Since  these  particles  are  thought  to  have  moved  like  miniature 

planets,  they  are  called 
planetesimals.  Each 
planetesimal  is  con- 
sidered to  have  moved 
in  its  own  orbit  around 
the  central  mass.  The 
planetesimals  did  not 
move  along  the  arms 
of  the  spiral,  but 
rather  crossed  them  at 
considerable  angles 
(Fig.  20).  "When  we 
see  a  spiral  we  do  not 
see  the  paths  which 
the  separate  masses 
have  described,  but 
the  positions  which 
they  occupy  at  the 
time.  In  the  present 
case  (Fig.  20)  if  a 
smooth  curve  is  drawn 
through  the  regions 
where  the  matter  is 
densest,  it  will  form  a 


Fig.  20 

Diagram  to  illustrate  the  formation  of  a  spiral 
nebula,  S,  sun;  S',  passing  star  whose  direc- 
tion of  motion  is  indicated  by  the  arrows. 
The  numbered  dotted  lines  show  the  paths 
followed  by  masses  pulled  out  from  S  by  S'. 
The  straight  dotted  lines  are  paths  which  the 
rupted  masses  would  have  followed  had  S' 
remained  stationary  in  the  respective  posi- 
tions indicated.  (Modified  after  Moulton 
by  W.  J.  M.) 


sort  of  double  spiral 
as  represented  by  the 
full  lines"  (Moulton). 
The  dotted  lines  in 
the  figure  represent  orbits  of  some  of  the  particles  or  knots.  Due 
largely  to  crossing  of  orbits,  the  knots  increased  in  size  by  a  gather- 
ing in  or  accretion  of  the  planetesimals.  Meteors,  which  now^strike 
the  earth,  are  thought  to  be  planetesimals  stilj^ga^ering  in,  though 
very  slowly  at  present.  The  spiral  orbits  of  the  loiots  (planets) 
gradually  gave  way  to  the  elliptical  orbits  due  to  a  sort  of  wrapping 
up  process  around  the  central  attracting  body  (sun). 


ORIGIN   OF  THE  EARTH  39 

The  origin  of  the  spiral  is  suggested  as  having  been  due  to  the 
disrupting  influence  of  the  central  body  or  sun  by  a  passing  star, 
the  disrupted  particles  or  masses  at  first  moving  straight  toward 
the  passing  star,  but,  because  of  change  in  position  of  the  passing 
body,  the  disrupted  masses  gradually  became  pulled  around  and 
their  paths  curved  into  spirals  as  shown  in  Fig.  20.  In  accord- 
ance with  the  principle  of  the  well-known  tide  producing  force, 
similar  disrupted  masses  must  also  have  shot  out  from  the  opposite 
side  of  the  sun  or  central  body.  Finally  when  the  passing  star  had 
so  far  gone  by  as  to  have  largely  lost  its  power  of  effectively  attract- 
ing the  sun,  the  spiral  orbits  of  the  planetesimals  gradually  became 
coiled  into  elliptical  or  nearly  circular  orbits  around  the  sun. 

Briefly,  according  to  this  hypothesis,  the  earth  was  never  a 
highly  heated  gas  and  never  necessarily  more  highly  heated  than 
at  present,  hence  sedimentary  as  well  as  igneous  materials  may  well 
be  expected  among  the  earliest  formed  rocks.  Instead  of  a  much 
larger  original  earth,  it  increased  in  size  by  accretion  of  planetesi- 
mals. With  increase  in  size  came  increase  in  force  of  gravity, 
causing  compression  of  the  earth's  matter  and  generation  of  more 
and  more  interior  heat.  Accompanying  this  increasing  pressure 
and  heat,  gases  (including  water  vapor)  were  driven  out  to  form  an 
atmosphere  which  gradually  became  larger  and  denser.  When 
the  water  vapor  had  sufficiently  accumulated,  precipitation  resulted 
to  initiate  the  hydrosphere. 

TABULAR  SUMMARY  OF  STAGES  OF  THE  EARTH'S  HISTORY  l 
9.  Cenozoic  era 


8.  Mesozoic  era 
7.  Paleozoic  era 
6.  Proterozoic  era 


Sedimentation  predominant  over  vulcanism. 
Higher  forms  of  organisms. 


c     A     v,  ( Vulcanism  predominant  over  sedimentation. 

a  I  Either  initial  or  at  least  only  very  simple  organisms. 

Nebular  hypothesis  Planetesimal    hypothesis 

4.  Hydrospheric  (oceanic)  stage.  Initial  hydrospheric  (oceanic)  stage. 

3.  Lithic  (congelation)  stage.  Initial  volcanic  stage. 

2.  Molten  stage.  Initial  atmospheric  stage. 

1.  Nebular  (gaseous)  stage.  Nuclear  (non-gaseous)  stage. 

1  Modified  after  Chamberlin  and  Salisbury. 


CHAPTER   IV 
THE  ARCHEOZOIC  ERA 

The  Oldest  Known  Geologic  Records.  —  In  earth  history,  as 
in  human  history,  the  recorded  events  of  earliest  times  are  fewest 
and  most  obscure,  and  hence  the  least  intelligible  of  all.  In  spite 
of  a  certain  disadvantage  in  beginning  with  the  least  known  part 
of  the  history  of  the  earth,  the  only  satisfactory  method  of  present- 
ing the  subject  is  "to  follow  the  natural  order  of  events.  This  has 
the  great  advantage  of  bringing  out  the  philosophy  of  the  history  — 
the  law  of  evolution"  (J.  Le  Conte).  The  earliest  known  geologic 
history  is  recorded  in  the  rocks  of  the  Archean  system.  While 
it  is  true  that  the  most  obscure  records  of  any  rock  system  are  here, 
partly  because  the  original  structures  of  these  rocks  have  generally 
been  so  profoundly  changed  (metamorphosed)  and  partly  because 
of  the  utter  absence  of  anything  like  determinate  fossils,  never- 
theless, certain  very  important  conclusions  regarding  the  earliest 
known  era  of  geologic  time  may  be  reached  through  a  study  of  the 
rocks  of  the  Archean  system.  The  present  state  of  our  knowledge 
does  not  warrant  the  subdivision  of  the  Archeozoic  into  two  or 
more  definite  periods  or  systems. 

General  Character  and  Origin  of  the  Archean  Rocks.  — "  Ar- 
chean Complex,"  "Basal  Complex,"  "Fundamental  Complex, "etc., 
are  all  terms  which  have  been  applied  to  the  rocks  of  the  Archean 
system  which  invariably  occupy  a  basal  position  with  reference  to 
all  other  rock  systems.  "The_Archean  system  is  a  crystalline 
complex  beneath  the  base  of  the  determined  sedimentary  succes- 
sion. .  .  .  The  United  States  Geological  Survey  has  restricted 
the  term  to  a  complex  of  basic  and  acidic  surface  and  deep-seated 
igneous  rocks,  of  schists  and  gneisses  in  part  derived  from  them  and 
in  part  of  unknown  origin,  and  of  shreds  and  small  masses  of  meta- 
morphosed sediments,  all  unconformably  below  and  older  than  the 
Algonkian  sedimentary  rocks,  which  are  the  lowest  series  in  which 
ordinary  stratigraphic  methods  have  been  applied.  Their  litho- 

40 


THINARCHEOZOIC  ERA  41 

logical  variations  are  many.  .  .  .  The  Archean  as  a  whole  is  homo- 
geneous in  its  heterogeneity."  1 

Briefly  stated,  the  Archean  system  exhibits  the  following  char- 
acteristics: (1)  So  far  as  observed,  it  always  shows  a  profound  un- 
conformity or  erosion  surface  at  its  summit;  (2)  its  lower  limit  or 
base  has  never  been  determined,  and  is  likely  inaccessible;  (3)  its 
thickness  is  very  great,  at  least  tens  of  thousands  of  feet,  and 
possibly  many  miles;  (4)  its  rocks  are  always  crystalline  and  usu- 
ally highly  metamorphosed  and  tilted  or  folded;  (5)  it  comprises 
a  most  heretogeneous  group  of  rocks,  often  intimately  associated, 
such  as  lavas  and  tuffs;  shales,  sandstones,  and' limestones  which 
have  been  highly  metamorphosed  to  schists  and  .-gneisses,  quartz- 
ites,  and  marbles;  some  beds  of  iron  ore;  arid  great  volumes  of 
granite  or  granitic  gneisses;  (6)  almost  invariably  igneous  rocks 
(granites  or  lavas)  greatly  predominate;.  (7)  it  never  contains 
distinct  fossils,  though  certain  evidences  of  life  do  exist;  and  (8) 
so  far  as  known  it  is  universally  present  at  or  under  the  earth's 
surface. 

The  Archean  has  been  more  or  less  studied  in  various  countries, 
and  the  above  named  features  always  appear  to  characterize  it. 
Caution  must  be  exercised,  however,  in  assigning  groups  of  rocks 
in  different  regions  to  the  Archean  merely  because  they  present 
some  or  many  of  these  characteristics.  Many  rocks  formerly 
classed  with  the  Archean  have  been  proved  to  be  of  later  age.  If 
rocks  with  all  the  characteristics  of  Archean  lie  below  definitely 
determined  (by  fossils)  Cambrian  strata,  and  are  separated  from 
the  Cambrian  by  a  great  series  of  sedimentary  or  metamorphic 
rocks  (Proterozoic),  then  we  may  be  pretty  certain  that  the  rocks 
belong  to  the  Archean  system.  If  crystalline  rocks  of  Archean 
appearance  are  directly  overlaid  by  Cambrian  strata,  or  by  Meso- 
zoic  strata,  the  crystalline  rocks  in  the  first  instance  may  be  either 
Archeozoic  or  Proterozoic,  and  in  the  second  instance  of  any  age 
preceding  the  Mesozoic  era. 

Subdivisions  of  the  Archean  System. — Wherever  studied  the 
Archean  appears  to  be  separable  into  two  pretty  distinct  groups 
or  classes  of  rocks,  namely,  (1)  a  volcanic  and  sedimentary  series, 
and  (2)  a  plutonic  series. 

The  volcanic  and  sedimentary  series  is  largely  composed  of 
metamorphosed  lava  flows  and  volcanic  tuffs;  some  massive  igne- 
1  Van  Hise  and  Leith:  U.  S.  Geol.  Survey  Bull,  360,  p.  26. 


42  HISTORICAL  GEOLOGY 

ous  rocks;  and  more  or  less  schist,  gneiss,  quartzite,  marble,  and 
some  iron  ore,  representing  all  the  common  types  of  sedimentary 
rocks  in  a  highly  metamorphosed  condition.  In  the  Lake  Superior 
district  this  series  is  called  the  Kewatin,  and  in  eastern  Canada 
and  the  Adirondacks  the  Grenville. 

The  plutonic  series  consists  of  tremendous  masses  of  deep- 
seated  igneous  rocks  which  are  mostly  red  to  gray  granites,  often 
of  different  ages,  and  at  times  with  more  basic  syenitic  to  even 
gabbroic  facies.  A  most  important  feature  of  this  series,  called 
the  Laurentian  in  the  Lake  Superior  district  and  in  eastern  Canada, 
is  the  fact  that  it  is  invariably  intrusive  into  the  first  or  lava- 
sedimentary  series.  Thus  as  regards  actual  position  in  the  earth's 
crust,  the  Laurentian  rocks  generally  lie  under  the  Kewatin  or 
the  Grenville,  but  since  the  contact  is  clearly  an  intrusive  one, 
the  law  of  superposition  cannot  here  be  applied  for  relative  age 
determination. 

The  following  tabular  summary  will  serve  to  make  clear  the 
subdivisions  of  the  Archeozoic  and  its  relation  to  the  Proterozoic 
in  a  portion  of  North  America  where  the  pre-Cambrian  rocks 
have  been  most  carefully  studied. 

Lake  Superior  District 

PALEOZOIC Cambrian 

Great  Unconformity 
(  2.  Keweenawan 
(unconformity) 

f  Upper  (Animikian) 


PBOTEROZOIC 
(Algonkian) 


1.  Huronian          I  Middle 


(unconformity) 


(unconformity). 
Lower 


Great  unconformity 

f  2.  Laurentian  granite 
ARCHEOZOIC       <       (Intrusive  into  Kewatin) 
[  1.  Kewatin  series 

Correlation  of  Archean  Rocks. — Because  of  the  complete 
absence  of  satisfactory  methods  of  correlation,  pre-Cambrian 
rocks  in  one  region  cannot  certainly  be  regarded  as  equivalent  to 
those  in  another  region  separated  from  it.  Thus  the  Grenville 
of  eastern  Canada  cannot  at  present  be  certainly  correlated  with 


THE  ARCHEOZOIC  ERA 


43 


the  Kewatin  of  the  Lake  Superior  region,  though  all  available  evi- 
dence strongly  points  to  such  a  correlation.  If  this  be  true,  it  is 
evident  that  the  whole  of  the  Proterozoic  is  absent  from  eastern 
Canada  and  the  Adirondacks  where  Upper  Cambrian  strata  rest 
upon  Grenville  and  Laurentian.  The  Grenville  is  essentially 
a  sedimentary  series,  many  thousands  of  feet  thick,  consisting 
largely  of  gneisses, 
quartzites,  and  crys- 
talline limestones, 
representing  what 
were  once  shales, 
sandstones,  and  lime- 
stones. These  are 
often  distinctly 
banded  because  of 
original  alternations 
in  deposition  of  the 
sediments,  and  some- 
times igneous  rocks 
of  Grenville  age  ap- 
pear to  be  mingled 
with  the  strata.  The 
Kewatin,  on  the  other 
hand,  is  essentially  a 
volcanic  series  of 


Fig.  21 

Archean  (Grenville)  sedimentary  gneiss  in  the  cen- 
tral Adirondacks.  Note  the  distinct  stratifica- 
tion. (W.  J.  Miller,  photo.) 


lavas  and  tuffs  with 
sediments  in  minor 
quantity. 

It  must  be  re- 
membered   that    the 

Archeozoic  represents  a  vast  length  of  time.  In  fact  the  Arche- 
ozoic era  may  have  been  longer  than  all  subsequent  time,  par- 
ticularly if  the  Plane tesimal  hypothesis  be  accepted,  because, 
according  to  that  view,  volcanic  extrusions  with  gradually  increas- 
ing accumulation  of  sediments  might  well  enough  have  taken 
place  long  before  the  earth  had  attained  anything  like  its  present 
size.  Realizing  the  very  great  thickness  of  rocks  and  time  which 
the  Archean  represents,  it  scarcely  seems  probable  that  its  base, 
or  even  the  base  of  that  portion  which  carries  sediments,  is  any- 
where exposed  to  view.  Bearing  these  things  in  mind  we  also  see 


44 


HISTORICAL  GEOLOGY 


that  though  in  many  regions  rocks  may  be  confidently  referred 
to  the  Archean  system,  nevertheless,  such  rocks  may  really  rep- 
resent vast  age  differences  within  that  system. 

Distribution   of   the   Archean.  —  So  far   as   known,    Archean 
rocks  appear  to  be  universally  present  at  or  below  the  earth's 


Fig.  22 

Map  showing  the  surface  distribution  of  pre-Cambrian  (Archeozoic  and 
Proterozoic)  rocks  in  North  America.  Largest  area  shown  by  dotted 
pattern;  smaller  areas  by  solid  black.  (Modified  by  W.  J.  M.  after 
Willis,  U.  S.  Geological  Survey.) 


THE  ARCHEOZOIC  ERA  45 

surface.  If  this  be  true,  and  all  evidence  strongly  favors  such  a 
view,  it  is  a  most  remarkable  characteristic  of  the  Archean,  since 
no  other  rock  system  has  such  a  distribution. 

A  rock  formation  may  be  so  distributed  in  the  earth's  crust  as 
to  be  present  (1)  at  the  surface  where  mere  superficial  deposits, 
such  as  mantle  rock,  glacial  drift,  etc.,  are  disregarded;  (2)  under 
cover  of  later  rocks,  but  where  its  presence  is  certainly  known  from 
surface  observations,  well  borings,  etc.,  and  (3)  under  cover  of  later 
formations,  but  where  its  presence  cannot  be  definitely  proved. 
Considering  all  regions  which  have  been  geologically  explored, 
the  Archean  is  estimated  to  appear  at  the  surface  over  about  one- 
fifth  of  the  land  area  of  the  earth. 

On  the  accompanying  map  (Fig.  22)  the  surface  distribution 
only  of  the  Archean  rocks  in  North  America  is  shown.  In  the 
Canadian  region  especially,  some  portions  mapped  as  Archean  may 
really  belong  to  the  Algonkian  or  even  later  systems,  because  so 
much  of  that  area  has  not  been  mapped  in  detail.  At  any  rate,  the 
map  shows  the  greatest  area  of  Archean  in  North  America  to  be 
around  Hudson  Bay.  This  vast  area  of  fully  2,000,000  square 
miles  consists  mostly  of  Archean.  Among  the  principal  smaller 
areas  are  those  of  Newfoundland,  New  England  states,  Adirondack 
Mountains,  Piedmont  Plateau  district,  Michigan,  Wisconsin, 
Minnesota,  and  numerous  small  areas  in  the  Rocky  Mountain 
district  (including  Alaska)  and  westward.  In  drilling  deep  wells 
in  many  places,  particularly  in  the  upper  Mississippi  Valley,  rocks 
of  the  Archean  complex  have  been  encountered,  and  so  we  may  be 
confident  of  the  presence  of  Archean  under  cover  of  thousands  of 
square  miles  of  later  rocks.  These  facts  of  distribution,  together 
with  the  fact  that  wherever  erosion  has  gone  deep  enough  the 
Archean  never  fails,  leave  little  room  for  doubt  concerning  the 
universal  presence  of  the  Archean  in  North  America. 

Foreign  Archean. — Judging  by  exposures  along  its  borders, 
Greenland  appears  to  be  largely  occupied  by  Archean  rocks. 

The  Highlands  of  Scotland  show  one  of  the  most  clearly 
exposed  areas  of  Archean  in  the  world,  and  detailed  studies  have 
shown  it  to  be  remarkably  like  that  of  the  Lake  Superior 
region. 

Scandinavia  exhibits  the  largest  area  of  Archean  rocks  in 
Europe,  and  considerable  study  has  shown  the  rocks  to  be  very 
similar  to  those  of  North  America. 


46  HISTORICAL  GEOLOGY 

Archean  rocks  are  also  known  in  Finland,  France,  Bavaria, 
Bohemia,  Spain,  India,  Australia,  China,  and  Japan. 

Life  and  Climate  of  the  Archeozoic  Era.  —  If  the  term 
"Archeozoic"  is  properly  applied,  rocks  of  that  age  should  show 
the  earliest  evidences  of  life.  Certain  beds  of  graphite;  beds  of 
iron  ore  which  were  derived  from  carbonates;  the  not  uncommon 
occurrence  of  numerous  flakes  of  graphite  in  certain  Archean 
schists,  gneisses,  and  crystalline  limestones;  and  the  very  existence 
of  the  limestone  itself,  altogether  quite  certainly  imply  the  exist- 
ence of  life  in  Archeozoic  time.  Limestone  has  sometimes  been 
of  chemical  origin,  but  the  presence  of  clearly  bedded  graphitic 
schists  and  crystalline  limestones  in  a  distinct  sedimentary  series 
almost  certainly  shows  the  influence  of  organisms  in  the  production 
of  both  the  graphite  and  the  limestone. 

As  to  the  character  of  the  life  notliing  definite  can  be  said,  not 
even  whether  it  was  plant  or  animal  or  both.  Nothing  like  deter- 
minable  fossil  forms  have  been  found  in  Archean  rocks,  and  even 
if  such  ever  were  present  they  must  have  been  obliterated  by  the 
intensfi^mejLamorphism  to  which  the  rocks  have  been  subjected. 
In  the  light  of  the  evolution  which  took  place  during  much  better 
known  geologic  time,  it  is  quite  certain  that  the  Archeozoic  or- 
ganisms must  have  been  much  sirrirjjjer  forms  than  those  of  the 
early  Paleozoic  which,  in  turn,  were  much  simpler  than  those  of 
the  present  day. 

All  we  can  say  about  Archeozoic  cluaaate  is  that,  during  some  of 
the  time  at  least,  it  was  favorable  for  the  existence  of  life  and  for 
ordinary  geologic  processes  such  as  prnsinn  and  sediiaaefitation. 

Economic  Products.  —  Iron  ore  in  workable  beds  occurs  in  the 
Archean  of  the  Lake  Superior  district. 

Granting  the  Archean  age  of  the  Grenville  series,  it  contains 
valuable  marble  deposits  as  at  Gouverneur  in  northern  New  York. 

Granites  intrusive  into  the  Grenville  contain  rich  magnetite 
deposits  in  Essex  county,  New  York. 

The  cobalt  and  nickel  deposits  of  Ontario,  Canada,  are,  in 
part  at  least,  associated  with  Archean  rocks. 


CHAPTER   V 
THE    PROTEROZOIC    ERA 

THE  Proterozoic  era,  represented  by  the  Algonkian  system  of 
rocks,  includes  the  time  between  the  Archeozoic  and  the  earliest 
Paleozoic  (Cambrian)  period,  the  Cambrian  system  comprising 
the  oldest  known  rock  system  with  abundant  fossils. 

Great  Unconformity  between  the  Archean  and  Algonkian 
Systems.  —  As  already  stated,  wherever  observations  have 
been  made  under  favorable  conditions,  the  summit  of  the  Archean 
•pmplex  appears  to  be  marked  by  a  profound  unconformity.  Such 
an  unconformity,  however,  cannot  be  universal  because  the  very 
fact  of  extensive  erosion  of  certain  areas  implies  the  deposition  of 
the  eroded  sediments  in  other  areas.  Such  sediments,  if 
would  contain  the  records  of  the  time  interval  indicated  by 
great  unconformity.  So  far  at  least,  this  sedimentary  record 
not  been  brought  to  light,  probably  either  because  (1)  these  sedi- 
ments were  deposited  in  ocean  basins  not  since  exposed  as  dry 
land;  or  (2)  these  sediments  are  not  at  present  exposed  to  view 
because  concealed  under  later  formations;  or  (3)  these  sediments 
have  not  been  recognized  as  such.  Also  it  is  not  at  all  unlikely 
that  some  or  even  many  of  these  sedimentary  areas  may  subse- 
quently have  become  land  areas  so  that,  as  a  result  of  erosion,  more 
or  less  of  the  sediments  were  again  removed  to  again  be  deposited 
as  Proterozoic  or  later  sediments.  Future  researches  may  bring 
to  light  some  of  the  now  "lost  records"  which  represent  the  great 
unconformity  or  time  gap  between  the  Archeozoic  and  Proterozoic. 

General  Character  and  Origin  of  the  Algonkian  Rocks.  — 
Emphasis  should  be  placed  upon  the  fact  that  the  Proterozoic  was 
the  first  era  during  which  ordinary  processes  of  weathering,  erosion, 
and  deposition  of  great  series  of  strata  became  dominant  processes, 
such  processes  having  been  dominant  ever  since.  Judging  by  the 
records,  the  Proterozoic,  on  one  hand,  was  marked  by  less  igneous 
activity  than  the  Archeozoic,  while,  on  the  other  hand,  it  was 
marked  by  distinctly  more  igneous  activity  than  any  subsequent 

47 


bion  of       f* 

3*0 


48  HISTORICAL  GEOLOGY 

era.     In  this  respect,  therefore,  the  Proterozoic  was  transitioi 
in  character. 

"The  Algonkian  system  as  this  term  is  used  by  the  Unitei 
States  Geological  Survey,  includes  sedimentary  formations  ana 
their  metamorphosed  equivalents  with  associated  igneous  rocks 
beneath  the  Cambrian  and  resting  upon  the  Archean  complex. 
It  includes  the  greater  part  of  the  sedimentary  rocks  of  pre-Cam- 
brian  age  and  practically  all  to  which  present  stratigraphic  methods 
have  been  found  to  apply,  though  it  contains  also  sedimentary 
rocks  so  deformed  and  metamorphosed  that  their  stratigraphy  is 
obscure.  .  .  .  The  Algonkian  sediments  are  known  to  contain  a 
few  fossils,  representing  the  earliest  forms  of  life  yet  found."  1 

An  important  feature,  especially  of  the  later  Proterozoic  rocks, 
is  the  frequent  presence  of  great  series  of  non-metamorphosed 
strata  which  are  therefore  the  oldest  known  unaltered  strata  of  the 
geologic  column.  Such  strata  include  all  common  types  of  sedi- 
mentary rocks  as  conglomerates,  sandstones,  shales,  and  limestones. 
Basal  conglomerates,  which  were  derived  from  the  lands  over 
which  the  Proterozoic  seas  at  various  times  spread  or  transgressed, 
are  frequently  found  at  the  bottoms  of  the  great  sedimentary  series. 
Other  great  series  of  Proterozoic  rocks  of  undoubted  sedimentary 
origin  are  more  or  less  metamorphosed  to  schists,  quartzites,  and 
crystalline  limestones.  The  earliest  Algonkian  sediments  were 
derived  from  exposed  portions  of  the  Archean,  while  later  Algon- 
kian sediments  may  have  been  derived  either  from  exposed  Ar- 
chean or  older  Algonkian.  That  the  processes  of  sedimentation 
during  the  Proterozoic  era  were  essentially  the  same  as  those  of 
today  is  clearly  proved  by  the  very  character  of  the  sediments, 
the  typical  stratification  to  even  lamination,  shallow-water 
marks,  etc. 

Beside  the  sedimentary  deposits,  there  is  much  igneous  rock 
both  in  the  forms  of  intrusions  into  the  sediments,  and  as  extru- 
sions or  lava-flows.  In  the  latest  (Keweenawan)  Algonkian  series 
of  the  Lake  Superior  district  lava  flows  or  beds  predominate  over 
sediments,  while  in  the  older  Algonkian  series  igneous  rocks  (either 
intrusive  or  extrusive)  may  locally  predominate. 

In  addition  to  the  frequent  metamorphism,  the  Algonkian  rocks 
have  often  been  subjected  to  great  deformative  movements  in  the 
earth's  crust  so  that  the  rocks  have  either  been  tilted  or  highly 
1  Van  Hise  and  Leith:   U.  S.  Geol.  Survey  Bull.  360,  1909,  p.  32. 


THE  PROTEROZOIC  ERA 


49 


Ided.     Sometimes  they  have  been  infolded  among  the  Archean 
•ocks. 

Subdivisions  of  the  Algonkian.  —  In  many  regions  where 
detailed  studies  have  been  made,  the  Algonkian  system  may  be 
subdivided  into  from  two  to  four  series  separated  by  distinct 
unconformities.  In  some  places  only  one  series  has  been  recog- 
nized. At  present  no  such  subdivision  into  series  has  a  world- 
wide or  even  continent- wide  application.  Generally  each  of  these 
series  shows  a  thickness  of  at  least  a  few  thousand  feet,  while  the 
whole  Algonkian  system  has  a  maximum  thickness  of  many  thou- 
sands of  feet,  or,  according  to  some  estimates,  at  least  ten  miles  in 


Fig.  23 

Diagram  showing  the  principal  subdivisions  of  the  Proterozoic  and  their  re- 
lation to  the  Archeozoic  in  the  Lake  Superior  district.  AR,  Archean; 
H,  Huronian;  A,  Animikean;  K,  Keweenawan.  (From  Chamberlin  and 
Salisbury's  " Geology,"  permission  of  Henry  Holt  and  Company.) 

the  Lake  Superior  district.  These  subdivisions  or  series  of  Algon- 
kian rocks  will  perhaps  be  best  understood  by  briefly  describing 
a  few  of  the  better  known  regions. 

Lake  Superior  District.  —  One  of  the  best  and  most  carefully 
studied  Algonkian  districts  in  the  world  is  that  around  Lake 
Superior.  Algonkian  rocks  are  there  divided  into  four  distinct, 
largely  sedimentary  series  separated  from  each  other  by  uncon- 
formities, and  named  Lower  Huronian,  Middle  Huronian,  Upper 
Huronian  (Animikian),  and  Keweenawan  (Fig.  23).  At  some 
localities  not  all  of  these  series  are  represented.  The  relations  of 
these  series  to  each  other  and  to  the  Archeozoic  below  and  Pale- 
ozoic above  are  brought  out  in  the  tabular  arrangement  given  on 
page  42.  As  indicated  by  the  unconformities,  the  deposition  of 
each  series  was  succeeded  by  emergence  of  the  region  accompanied 
by  erosion,  and  this  in  turn  followed  by  submergence  accompanied 


50  HISTORICAL  GEOLOGY 

by  deposition  of  the  next  series.  Such  repeated  changes  of  relative 
level  between  land  and  sea,  as  here  recorded  for  Proterozoic  time, 
are  among  the  most  common  and  important  phenomena  of  geo- 
logic history. 

The  Huronian  rocks  are  principally  quartzites,  slates,  schists, 
limestone  (usually  dolomitic),  and  some  conglomerates  and  beds 
of  iron  ore,  all  of  which  are  metamorphosed  sediments.  Locally 
some  of  these  beds  have  not  been  metamorphosed.  Considerable 
masses  of  igneous  rock,  some  intrusive  and  some  lava  flows,  also 
are  included  among  the  Huronian  rocks.  The  Lower  and  Middle 
Huronian  are  usually  much  more  metamorphosed  and  folded  than 
the  Upper,  the  latter  being  at  times  scarcely  at  all  deformed  or 
metamorphosed.  Estimates  show  the  aggregate  (maximum) 
thickness  of  the  Huronian  rocks  to  be  no  less  than  two  or  three 
miles. 

The  Keweenawan,  or  latest  Proterozoic  series,  is  characterized 
by  a  great  preponderance  of  lava  flow  which  constitute  the  lower 
portion  of  the  series;  are  prominent  in  its  middle  portion;  and  are 
practically  absent  from  the  upper  portion.  Some  idea  of  the  stu- 
pendous and  continuous  volcanic  activity  of  Keweenawan  time 
may  be  gained  from  the  fact  that  lava  sheets,  mostly  not  over  a 
hundred  feet  thick  each,  accumulated  to  a  depth  of  at  least  five4)r 
six  miles.  Between  some  of  the  later  lava  sheets,  thin  beds  of 
sediment  were  deposited,  while  the  upper  part  of  the  Keweenawan 
consists  altogether  of  sediments,  chiefly  conglomerates  and  sand- 
stones. The  sediments  are  estimated  to  have  a  thickness  of  about 
three  miles,  so  that  the  whole  Keweenawan  series  must  be  some 
eight  or  ten  miles  thick. 

Rocky  Mountain  Region.  —  Perhaps  the  largest  known  area  of 
Algonkian  rocks  in  North  America  is  that  in  the  Rocky  Mountains 
of  the  northern  United  States  and  southern  British  Columbia. 
These  rocks  generally  rest  upon  eroded  Archean  and  they  are 
overlain  unconformably  by  Cambrian  or  still  younger  strata.  The 
rocks  consist  mostly  of  quartzites,  sandstones,  shales,  and  lime- 
stones, more  or  less  associated  with  igneous  rocks.  Their  thick- 
ness is  at  least  two  or  three  miles.  Some  of  the  strata  (in  Montana) 
contain  fossils.  In  central  Montana  at  least  the  Algonkian  strata 
appear  to  have  been  upturned,  folded,  and  somewhat  eroded 
before  the  deposition  of  the  Cambrian.  At  present  no  satis- 
factory subdivision  of  these  rocks  has  been  determined. 


THE  PROTEROZOIC  ERA  51 

Grand  Canyon  of  the  Colorado.  —  In  the  Grand  Canyon  of  the 
Colorado  River,  there  are  excellent  exposures  of  Algonkian  rocks 
with  their  relations  to  the  Archeozoic  and  and  Paleozoic  well 
exhibited  (Fig.  24).  The  Archean  complex  comprising  "  granites, 
gneisses,  and  schists  was  almost  completely  leveled  before  the 
deposition  of  the  next  overlying  series.  The  unconformably  over- 
lying series  is  the  Grand  Canyon  (Algonkian)  series,  11,950  feet 
thick,  consisting  of  two  groups  —  the  Unkar,  6,830  feet  thick, 
and  the  Chuar,  5,120  feet  thick.  The  Unkar  group  consists  of 
sandstones  and  limestones  interstratified  with  basalts,  and  has 
at  its  base  a  conglomerate.  .  .  .  Resting  upon  the  Unkar  group 
with  a  slight  unconformity  is  the  Chuar  group.  It  consists  of 
shales,  sandstones,  shaly  limestones,  and  limestones. "  1 

Correlation  of  Algonkian  Rocks. — The  statements  made  regard- 
ing the  difficulties  of  correlating  the  Archean  rocks  apply  almost 
equally  well  here.  Algonkian  rocks  being,  however,  more  largely 
distinctly  sedimentary,  and  usually  not  so  severely  metamor- 
phosed; usually  separated  into  series  by  well-defined  unconform- 
ities; and  with  fossils  gradually  coming  to  light  in  certain  of  the 
uppermost  series,  afford  a  much  more  satisfactory  basis  for  apply- 
ing ordinary  stratigraphic  methods  of  correlation  than  do  the 
Arbhean  rocks.  Remarkable  similarities  such  as  exist  between 
the  Superior  and  Grand  Canyon  Algonkian  series  are  highly  sug- 
gestive of  correlation,  though  far  from  actually  demonstrable  at 
present.  Lithologic  and  structural  similarities  alone  are  not  safe 
methods  of  correlation.  Future  studies,  however,  are  quite  likely 
to  yield  satisfactory  results  in  some  cases  at  least. 

Not  only  the  lack  of  fossils,  but  also  the  vast  length  of  time  of 
the  Proterozoic  era,  are  great  difficulties  in  the  way  of  correlation. 
Considering  the  time  necessary  for  the  deposition  of  the  tremendous 
thickness  of  Algonkian  rocks,  and  the  several  long  unrecorded 
time  intervals,  it  seems  reasonable  to  believe  that  the  Proterozoic 
era  was  fully  as  long  as  the  Paleozoic.  Hence  two  similar  series  of 
Algonkian  rocks  resting  directly  upon  the  eroded  surface  of  the 
Archean  in  widely  separated  regions  may  in  reality  be  far  different 
in  age  because  the  Archean  in  one  region  may  have  remained 
unsubmerged  very  much  longer  than  in  the  other.  Or  again,  an 
Algonkian  series  of  one  district  may  actually  have  been  deposited 
during  a  time  represented  by  an  unconformity  in  another  district, 
1  Van  Hise  and  Leith:  U.  S.  Geol.  Survey  Bull.  360,  1909,  p.  778. 


!&«« 
III! 


^|| 

G    02  — *    ie 

-H     ^       OJ       P 

^s-15 


THE  PROTEROZOIC  ERA  53 

Distribution  of  the  Algonkian.  —  As  already  stated,  perhaps  . 
the  largest  Algonkian  area  in  North  America  is  that  of  the  Rocky 
Mountains  in  the  northern  United  States  and  southern  British 
Columbia.  The  well-known  Lake  Superior  district  of  Algonkian  is 
also  of  large  extent.  There  are  considerable  areas  in  eastern  Can- 
ada west  of  Hudson  Bay,  and  smaller  areas  in  Newfoundland, 
Nova  Scotia,  the  Piedmont  Plateau,  at  several  places  in  the  Missis- 
sippi Basin,  Texas,  Arizona  (especially  in  the  Grand  Canyon), 
Nevada,  and  at  various  places  in  the  Rocky  Mountain  system 
throughout  the  United  States  and  Canada. 

Foreign  Algonkian.  —  Algonkian  rocks  are  thought  to  exist  in 
all  continents.  In  the  Highlands  of  Scotland,  the  Torridon  sand- 
stones and  shales,  about  10,000  feet  thick,  are  quite  certainly  of 
Algonkian l  age,  since  they  lie  unconf ormably  between  the  Archean 
complex  below  and  well-defined  Cambrian  above. 

The  large  pre-Cambrian  rock  area  in  Scandinavia,  which  in 
many  respects  is  similar  to  that  of  Scotland,  also  contains  consid- 
erable bodies  of  sediments  (at  least  10,000  feet  thick)  of  Algonkian 
age,  the  term  " Algonkian"  having  actually  been  applied  there. 
As  in  the  Lake  Superior  region,  iron  ore  occurs  in  some  of  the 
Swedish  Algonkian. 

In 'Finland,  France,  Germany,  Spain,  and  probably  in  India 
and  Brazil,  Algonkian  rocks  are  known. 

It  should  be  noted  that  in  several  of  the  foreign  countries 
there  appears  to  be  a  division  of  the  Algonkian  system  into  at 
least  two  series  separated  by  unconformities. 

Life  and  Climate  of  the  Proterozoic  Era. — As  has  been  men- 
tioned, determinable  fossils  have  been  found  in  the  upper  Algon- 
kian rocks  of  Montana  and  the  Grand  Canyon  of  the  Colorado. 
These  fossils  include  Worm  tracks,  a  Brachiopod,  and  fragments 
ol  'Crustaceans.  In  EuTdpe  a  few  similar  fossils  have  been  found. 
Recently  the  discovery  of  Radiolarians  in  the  Proterozoic  rocks 
of  France  has  been  reported.  "The  traces  of  pre-Cambrian  life, 
though  very  meager,  are  sufficient  to  indicate  that  the  develop- 
ment of  life  was  well  advanced  long  before  Cambrian  time  began. 
.  .  .  Stratigraphically,  this  fragment  of  what  must  have  been  a 
large  fauna  occurs  over  9,000  feet  beneath  an  unconformity  at  the 
base  of  the  upper  portion  of  the  Lower  Cambrian  in  northern 

1  Thus  far  the  term  "Algonkian"  has  not  often  been  used  in  foreign 
countries. 


54 


HISTORICAL  GEOLOGY 


Montana. "  1  More  and  still  older  forms  are  quite  likely  to  be 
discovered,  though  the  remains  thus  far  found  are  those  of  very 
thin-shelled  animals  and  hence  not  so  favorable  for  fossilization. 
Most  animals  of  the  time  were  probably  without  shells  or  other 
hard  parts. 

Very  recently  Walcott  has  described  a  number  of  species  of 
calcareous  Algae  from  the  Belt  series  (Algonkian)  of  Montana 


Fig.  25 

Part  of  a  pre-Cambrian  (Huronian)  Alga.  This  is  one  of  the  oldest 
known  definitely  determinable  fossils.  After  Geol.  Sur.  Canada. 
(From  Schuchert's  "Historical  Geology,"  permission  of  John 
Wiley  and  Sons.) 

and  one  (discovered  by  Lawson)  from  a  Huronian  limestone  of 
western  Ontario,  this  latter  being  the  oldest  known  well  preserved 
fossil.  These  Algae  were  very  simple  plants  (Thallophytes)  which 
lived  in  water.  They  were  hemispherical  or  cylindrical  bodies 
which  secreted  crudely  concentric  layers  of  carbonate  of  lime 
from  1  to  15  inches  in  diameter.  They  occur  in  distinct  beds 
through  hundreds  or  even  thousands  of  feet  of  Algonkian  lime- 
stones. 

Graphite  and  carbonaceous  material  so  often  disseminated 
through  the  shales  and  schists  almost  certainly  indicate  the  ex- 
istence of  life.  Likewise  beds  of  limestone  (even  near  the  base  of 

.      i  C.  D.  Walcott:  Jour.  Geol.,  Vol.  17,  1909,  p.  196. 


THE  PROTEROZOIC  ERA  55 

the  Algonkian)  and  iron  ore  are  rarely  ever  known  to  have  been 
formed  except  through  the  agency  of  organisms. 

Since  the  great  masses  of  Proterozoic  sediments  are  of  quite 
the  usual  sort  like  those  formed  in  later  eras,  and  since  life  surely 
existed,  we  can  be  certain  that  the  climate  of  the  time  was  favor- 
able for  the  operations  of  ordinary  geologic  processes  and  hence 
not  fundamentally  different  from  that  of  comparatively  recent 
geologic  time. 

According  to  a  discovery  made  a  few  years  ago,  there  is  posi- 
tive evidence  for  considerable  glaciation  in  Canada  during  early 
Algonkian  time.  Conglomerate  beds  at  the  base  of  the  Huronian 
are  regarded  as  of  glacial  origin  since  there  are  "angular  and  sub- 
angular  boulders  of  all  sizes  up  to  cubic  yards,  enclosed  in  an 
unstratified  matrix.  These  boulders  are  often  miles  from  any 
possible  source.  Recently,  striated  stones  have  been  broken  out 
of  their  matrix  in  the  Lower  Huronian  of  the  Cobalt-Silver  region, 
giving  still  stronger  proofs  that  the  formation  is  ancient  boulder 
clay."  l  A  climatic,  condition  favorable  for  glaciation  so  early  in 
the  earth's  history  is,  to  say  the  least,  distinctly  opposed  to  ideas 
of  climate  of  such  early  geologic  time  based  upon  the  Laplacian 
^ 


Economic  Products.  —  The  greatest  iron  mining  region  in  the 
world  is  the  Lake  Superior  district  in  Minnesota,  Michigan,  and 
Wisconsin.  Some  of  these  iron  ores  are  in  the  Archean,  and  some 
in  the  older  Huronian  rocks,  but  the  principal  deposits  are  in  the 
Upper  Huronian.  These  iron  ores  occur  as  thick  beds  in  the  sedi- 
mentary series.  Often  the  iron  ore  deposits  have  been  enriched 
by  the  work  of  underground  waters.  The  Lake  Superior  district 
produces  many  millions  of  tons  of  iron  ore,  or  far  more  than  the 
production  of  any  foreign  country. 

The  greatest  deposits  of  native  copper  in  the  world  are  in  the 
Keweenawan  series  on  Keweenaw  Point,  Michigan.  Copper  has 
been  found  in  small  quantities  in  the  lava  beds,  and  underground 
waters  have  dissolved  out  this  copper  and  deposited  it  in  more 
concentrated  form  in  fissures  and  openings  of  the  rock,  and  also  in 
porous  conglomerates.  Immense  quantities  of  native  copper  have 
been  mined  here  during  the  past  forty  years. 

i  A.  P.  Coleman:  Jour.  GeoL,  Vol.  16,  p.  149. 


PALEOZOIC  ERA 
CHAPTER  VI 

THE    CAMBRIAN    PERIOD 

THE  Cambrian  represents  the  earliest  period  of  the  great  Pal- 
eozoic era,  and  the  rocks  which  make  up  the  Cambrian  system 
include  the  oldest  known  of  the  normal  fossiliferous  strata.  Since 
these  strata  are  the  oldest  which  carry  abundant  organic  remains, 
it  follows  that  they  are  the  earliest  formed  rocks  to  which  the  ordi- 
nary methods  of  subdividing  and  correlating  rock  masses  can  be 
applied.  From  the  Cambrian  on,  the  legible  records  of  events  of 
earth  history  are  far  more  abundant  and  less  defaced  than  those  of 
pre-Cambrian  time.  From  now  on  we  shall  be  able  to  trace  the 
changing  outlines  of  the  relief  features  of  the  continents  and  the 
evolution  of  organisms  with  some  degree  of  definiteness  and  satis- 
faction, though  a  vast  amount  of  work  yet  remains  to  be  done  both 
as  regards  discovery  of  new  records  and  the  interpretation  of 
records  old  and  new. 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

The  oldest  Paleozoic  rocks  were  first  carefully  studied  independ- 
ently in  the  British  Isles  by  the  two  able  geologists,  Sedgwick  and 
Murchison,  before  the  middle  of  the  nineteenth  century.  Murchi- 
son  applied  the  name  " Silurian"  to  the  great  series  of  oldest 
fossiliferous  strata  and  divided  them  into  Lower  and  Upper 
Silurian.  Sedgwick,  however,  considered  that  the  very  oldest 
fossil-bearing  rocks  should  be  separately  designated,  hence  his 
application  of  the  term  " Cambrian,"  from  Cambria  an  old  Latin 
name  for  a  part  of  Wales.  The  Cambrian  is  now  recognized  the 
world  over  as  the  oldest  Paleozoic  system. 

In  North  America  a  threefold  subdivision  of  the  Cambrian 
system  is  recognized  as  follows : 

56 


THE  CAMBRIAN  PERIOD  57 


General  New  York  and  New  England 

Little  Fall 
Potsdam  s 

Stissing  limestone. 


3.  Upper  Cambrian Saratogan  (Croixian)  series  /  ^ittl(?  FaUs  dolomite. 

(Dikellocephalus  fauna) 
2.  Middle  Cambrian Acadian  series 


(Paradoxides  fauna) 
1.  LowerCambrian.      .Georgian  (Waucobian)  series 

(Olenellus  fauna)  Poughquag  quartzite. 


, 


In  the  typical  regions  these  strata  are  superposed 
the^pilifirjin  regular  order  wit  hou  tlrnmn  form  i  t.y  .  but  careful  study 
has  shown  that,  passing  upward  in  the  system  of  strata,  there  is 
a  gradual  change  in  the  character  of  the  fossils,  particularly  the 
Trilobitesjwhich  are  so  common  and  widespread  in  the  rocks.  Thus 
the  Lower  Cambrian  strata  are  generally  characterized  by  the 
Trilobite  genus  Olenellus,  with  its  various  species,  and  this  charac- 
teristic assemblage  of  Trilobites  is  called  the  Olenellus  fauna.  This 
does  not  mean  that  Olenellus  invariably  occurs  in  Lower  Cambrian 
strata,  or  that  other  genera  of  Trilobites  and  other  fossils  may  not 
be  present.  In  a  similar  way  the  Paradoxides  and  the  Dikello- 
cephalus faunas  are  the  chief  characteristics  of  the  Middle  and 
Upper  Cambrian  respectively.  Such  stages  or  lifft  /QJIP.S-  in  the 
geologic  column  are  commonly  referred  to  as  horizons..  It  should 
be  made  clear  that  the  genus  Olenellus  became  extinct  before  the 
Middle  Cambrian  strata  were  deposited;  the  Paradoxides  dis- 
appeared before  the  Upper  Cambrian  was  deposited;  and  the 
Dikellocephalus  before  the  deposition  of  the  succeeding  Ordovi- 
cian  strata,  though  it  is  not  meant  that  sharp  lines  separate  these 
faunas.  Thus  each  of  the  faunas  becomes  an  important  geologic 
time  or  horizon  marker.  A  representative  of  each  of  these  genera 
of  Trilobites  is  shown  in  Fig.  39. 

These  principles,  here  laid  down  as  a  basis  for  the  subdivision 
of  the  Cambrian  system,  apply  equally  well  to  the  succeeding  rock 
systems,  though  many  organisms  other  than  Trilobites  are  used 
for  the  purpose. 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  On  the  accompanying  map  (Fig.  26) 
the  surface  distribution  of  Cambrian  rocks  is  shown,  that  is  to  say 
the  locations  of  the  areas  in  which  Cambrian  strata  are  known  to 
outcrop.  The  principal  areas  are  seen  to  be  in  Newfoundland, 


58 


HISTORICAL  GEOLOGY 


New  York,  through  the  Appalachian  range,  south  of  Lake  Superior, 
southeastern  Missouri,  Oklahoma,  central  Texas,  and  at  various 


Fig.  26 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Cambrian,  and 
some  very  closely  associated  Lower  Ordovician,  strata  in  North  America. 
(Modified  by  W.  J.  M.  after  Willis,  U.  S.  Geological  Survey.) 

places  in  the  Rocky  Mountain  region.  Because  Cambrian  rocks 
have  so  often  been  removed  by  erosion,  or  have  been  so  largely 
covered  by  later  sediments,  or  highly  folded  so  that  outcropping 


THE  CAMBRIAN  PERIOD  59 

edges  only  are  now  exposed,  the  surface  distribution  as  indicated 
on  the  map  fails  to  give  any  adequate  idea  of  the  former  or  even 
present  real  extent  of  strata  of  this  age.  Thus  Cambrian  strata 
are  definitely  known  to  have  been  almost  completely  removed 
from  several  thousand  square  miles  of  the  northern  New  York 
region,  and  Cambrian  rocks  have  certainly  been  similarly  removed 
from  many  other  regions.  Agairi,  the  distribution  of  the  outcrops, 
together  with  many  deep  well  sections  (Fig.  27),  make  it  certain 
that  Cambrian  strata  concealed  under  nearly  horizontal  later  strata 
spread  across  much,  if  not  all,  of  the  Mississippi  Valley  from  the 
Rockies  to  the  Appalachians,  while  in  the  Appalachian  Mountains 
Cambrian  rocks  are  really  much  more  extensive  than  the  mere 
outcropping  edges  of  the  upturned  strata.  There  is  no  reason, 
however,  to  think  that  the  vast  area  of  pre-Cambrian  rock  around 
Hudson  Bay,  the  Atlantic  Coast  from  New  Jersey  southward,  the 
Pacific  Coast  including  the  Coast  Range,  Sierra  Nevada,  and 
Cascade  Mountain  areas,  were  ever  covered  by  the  Cambrian 
sea. 

The  difference  in  the  distribution  of  the  Lower  and  Upper 
Cambrian  strata  is  a  prime  consideration.  Thus  the  Lower  Cam- 
brian is  entirely  absent  from  the  whole  Mississippi  Valley  except 
probably  its  southern  border.  Otherwise  the  same  general  areas 
are  occupied  by  both  Lower  and  Upper  Cambrian  strata. 

Character  of  the  Rocks.  —  Cambrian  rocks  consist  very  largely 
of  shallow  water  sediments  such  as  conglomerates,  sandstones 
(Fig.  28),  and  shales,  with  well-preserved  ripple  marks  very 
common.  Deeper  or  clearer  water  deposits  such  as  limestone, 
are,  however,  important  in  the  Appalachians,  Vermont,  Nevada, 
and  British  Columbia.  When  these  sediments  were  deposited 
in  the  Cambrian  sea  they  were  like  ordinary  gravels,  sands,  marls, 
and  limy  oozes  now  forming  in  the  ocean,  especially  over  the 
continental  shelf  areas  and  their  borders.  Since  their  deposition 
they  have  been  changed  into  the  corresponding  harder  rocks  such 
as  conglomerates,  sandstones,  shales,  and  limestones,  or,  in  some 
cases  as  in  New  England,  metamorphosed  into  quartzites,  schists 
or  slates,  and  crystalline  limestones  (marbles).  In  many  regions 
the  Cambrian  strata  have  been  highly  folded  and  faulted. 

Thickness  of  the  Cambrian  and  Igneous  Rocks.  —  The  thick- 
ness of  Cambrian  strata  in  North  America  varies  from  less  than 
1,000  feet  to  a  maximum  of  over  10,000  feet.  North  American 


HISTORICAL    GEOLOGY 


|I||l!li§ii!i|  I     i     I     f     I  :§     I 

Fig.  27 

Geologic  section  through  northeastern  Iowa,  showing  how  character,  thick- 
ness, and  distribution  of  deeply  buried  rock  formations  can  be  determined 
by  a  comparison  of  well  records.  St.  Lawrence  and  Jordan  formations  are 
Cambrian;  Oneota  to  Maquoketa  inclusive  are  Ordovician;  and  above 
these  are  Silurian  and  Devonian  strata  as  indicated.  (After  W.  H.  Norton, 
U.  S.  Geological  Survey.) 


THE  CAMBRIAN  PERIOD  61 

Cambrian  is  singularly  free  from  igneous  rocks  and  thus  presents  a 
remarkable  contrast  with  the  preceding  eras. 


PHYSICAL  HISTORY 

Great  Basal  Unconformity.  —  We  have  already  learned  that  a 
profound  and  seemingly  almost  universal  unconformity  separates 
the  Archean  and  Algonkian  rocks.  Another  great  unconformity 
separates  the  Algonkian  and  Paleozoic  rocks.  Cambrian  strata 
rarely,  if  ever  fail  to  rest  upon  the  eroded  surfaces  of  either  the 
Archean  or  the  Algonkian.  C.  D.  Walcott  has  recently  (1914) 
stated  that  no  definitely  proved  transition  rocks  between  the 
Cambrian  and  pre-Cambrian  are  known  in  North  America.  It 
has  been  definitely  proved,  as  for  example  in  the  Adirondack  region, 
to  be  quite  the  rule  that  the  Cambrian  sediments  not  only  rest  upon 
an  eroded  surface  of  older  rocks,  but  that  the  surface  of  these 
latter  had  been  worn  down  to  the  condition  of  a  more  or  less  well- 
developed  peneplain.  Accordingly,  just  before  and  during  early 
Cambrian  tiniej  most  of  North  America  must  have  been  dry  land^ 
suffering  erosion.  Conglomerates  containing  pebbles  of  the  older 
rocks  are  of  very  common  occurrence  at  the  base  of  the  Cambrian 
sediments.  The  great  duration  of  this  erosion  interval  which  pro- 
duced such  a  profound  unconformity,  not  only  in  North  America 
but  in  other  continents  as  well,  is  regarded  as  one  of  the  greatest 
physical  events  of  its  kind  in  the  history  of  the  earth  since  the 
beginning  of  Paleozoic,  or  rather  late  Proterozoic,  time. 

Early  Cambrian.  —  "The  great  physical  event  of  the  Cam- 
brian period  in  North  America  was  the  progressive  submergence 
of  the  continent "  (Chamberlin  and  Salisbury) .  As  we  have  already 
learned,  such  a  submergence  may  have  been  produced  either  by 
rising  sea  level,  or  subsidence  of  the  land,  or  both.  In  the  case  of 
the  Cambrian  submergence  there  appears  to  be  no  escape  from  the 
conclusion  that  a  rise  of  the  sea  was  an  important  factor,  since  the 
development  of  such  an  extensive  peneplain  surface  implies  that 
the  continent  must  have  remained  almost  unaffected  by  diastrophic 
movements  for  a  long  time,  and  the  tremendous  volume  of  material 
removed  and  dumped  into  the  sea  must  have  very  appreciably 
raised  its  level. 

Wherever  Lower  Cambrian  marine  strata  (actually  exposed  or 
concealed)  rest  directly  upon  pre-Cambrian  rocks  we  can  be  sure 


Fig.  28 

Upper  Cambrian  (Potsdam)  sandstone  in  the  Ausable  Chasm  of  northeastern 
New  York.  The  rock  is  distinctly  stratified  and  full  of  ripple-marks. 
(Courtesy  of  the  New  York  State  Museum.) 


THE   CAMBRIAN  PERIOD  63 

that  such  areas  were  submerged  under  the  early  Cambrian  sea, 
because  Lower  Cambrian  strata  could  have  formed  only  during 
that  time.  To  these  areas  must  be  added  still  others  from  which 
the  rocks  have  been  removed  by  erosion.  Further,  since  the  later 
Cambrian  strata  almost  invariably  rest  in  perfect  conformity  ^jGr 
upon  the  earlier,  we  can  be  sure  that  any  region  occupied  by  later,  «& 
but  not  earlier,  Cambrian  rocks  was  never  covered  by  the  earlier 
Cambrian  sea  because  the  conformity  proves  that  there  was  no 
erosion  interval  during  which  any  of  the  earlier  Cambrian  strata 
were  removed  before  the  deposition  of  the  later.  Again,  some  other 
areas  were  almost  certainly  dry  land  during  early  Cambrian  time 
because  there  is  not  the  slightest  evidence  of  any  sort  that  deposi- 
tion went  on  over  those  areas  during  that  time.  The  principles 
here  set  forth  are  of  fundamental  importance  in  constructing  a 
paleogeographic  map  of  North  America  for  early  Cambrian  time, 
and  the  same  principles  must  be  kept  in  mind  in  considering  the 
paleogeography  of  any  given  region  during  succeeding  time. 

In  accordance  with  the  above  principles,  we  can  be  sure  that 
the  general  outlines  of  the  continent  of  North  America  in  early 
Cambrian  time  were  much  as  indicated  upon  the  accompanying 
map  (Fig.  29).  The  great  central  region,  between  what  are  now 
the  Rocky  Mountains  on  the  west  and  the  Appalachian  Mountains 
and  St.  Lawrence  Basin  on  the  east,  was  dry  land. 

Bordering  this  central  mass  on  the  west  and  on  the  east  were 
two  long,  narrow  sounds  or  mediter  anean  seas,  the  one  on  the  west 
covering  the  present  site  of  the  Rocky  Mountains,  and  the  one  on 
the  east  the  present  sites  of  the  Appalachian  Mountains  and  the 
Champlain  and  St.  Lawrence  Valleys.  Lower  Cambrian  sediments 
were  accumulated  in  these  sounds. 

Along  the  Atlantic  side,  and  bordering  the  eastern  sound,  an 
important  land  mass,  called  "  Appalachia, "  extended  from  New 
Brunswick  southward  to  the  Gulf  of  Mexico  and  doubtless 
included  much  of  the  present  continental  shelf  area.  As  we  shall 
learn,  Appalachia  apparently  persisted,  though  with  more  or  less 
changing  outlines,  throughout  the  Paleozoic  era. 

Along  the  Pacific  side,  and  bordering  the  western  sound,  there 
were  considerable  (possibly  mostly  continuous)  land  masses  which 
separated  the  sound  from  the  Pacific  ocean. 

Middle  and  Late  Cambrian.  —  During  middle  and  late  Cam- 
brian time  more  and  more  of  the  continent  gradually  became  sub- 


MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA,  MORE  LIKELY  LAND 


Fig.  29 

Paleogeographic  map  of  North  America  during  Lower  (early)  Cambrian 
time.  (Slightly  modified  after  Bailey  Willis,  courtesy  of  The  Journal  of 
Geology.) 


THE  CAMBRIAN  PERIOD  65 

merged  until  the  geographic  conditions  were  much  as  depicted 
upon  the  next  paleogeographic  map  (Fig.  30).  L  The  sea  trans- 
gressed northward  over  the  great  interior  land  to  about  the  north- 
ern border  of  the  United  States,  the  early  Cambrian  sounds  merging 
into  this  vast  interior  sea.  Around  Hudson  Bay  a  large  land 
area  still  persisted,  while  Appalachia,  and  the  lands  along  the 
Pacific  Coast,  remained  much  as  they  were  in  the  early  Cambrian. 
From  Wyoming  to  Arizona  a  considerable  area  appears  to  have 
remained  as  an  island  above  even  the  latest  Cambrian  sea.  The 
northward  trangression  of  this  great  interior  sea  is  clearly  estab- 
lished by  the  fact  that  studies  of  actual  outcrops  and  deep  well 
sections  show  successively  younger  and  younger  Cambrian  sedi- 
ments deposited  by  overlap  northward  upon  the  pre-Cambrian 
rock  surface.  We  also  know  that  this  interior  sea  was  shallow 
because  of  the  character  of  the  sediments  which  are  very  largely 
clastic  such  as  sandstones  and  shales  often  ripple  marked,  and  with 
conglomerates  at  the  base.  Some  heavy  limestone  beds  like  those 
in  eastern  New  York,  and  between  Virginia  and  Missouri,  tell  of 
clearer,  possibly  deeper,  water  in  those  places. 

Close  of  the  Cambrian.  —  The  physical  events  above  outlined 
prove  that  the  Cambrian  period  represents  a  long  time,  the  best 
estimates  ranging  from  2,000,000  to  3,000,000  years,  though  it 
should  be  emphasized  that  we  have  no  exact  standard  of  compari- 
son in  years.  The  only  object  in  presenting  such  figures  is  to  im- 
press upon  the  student  the  fact  of  the  vast  length  of  time  involved. 
Though  the  succeeding  periods  were  by  no  means  equal  in  duration, 
the  best  estimates  would  make  no  one  of  them  less  than  1,000,000 
years  long. 

Throughout  Cambrian  time,  and  even  at  its  close,  North 
America  was  not  affected  by  any  great  physical  disturbances  such 
as  vulcanism,  mountain  making,  or  emergence  of  large  areas  of 
land.  Only  locally,  as  for  example  in  northern  New  York,  and 
possibly  in  the  upper  Mississippi  Valley,  is  there  any  unconformity 

1  Recent  studies  seem  to  show  that  "near  the  close  of  Upper  Cambrian 
time  a  broad-spread  movement  resulted  in  the  temporary  withdrawal  of  the 
Cambrian  sea  from  the  upper  Mississippian  (valley)  area"  (C.  D.  Walcott, 
1914).  According  to  Ulrich  (Geol.  Soc.  Am.  Bull.,  Vol.  23,  pp.  627-647)  the 
time  represented  by  this  marine  retrogression  and  immediately  following 
transgression  should  be  called  a  separate  period  —  the  "Ozarkian."  Strata 
of  this  age  would  include  some  of  the  latest  Cambrian  and  some  of  the 
earliest  Ordovician. 


LATE  MIDDLE 
UPPER  CAMBRIAN 

— -  •  NORTH    AMERIC 


LEGEND 
OCEANIC  BASINS      

MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND,  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAND 
LANDS 
INDETERMINATE  AREAS 


Fig.  30 

Paleogeographic  map  of  North  America  during  late  Middle  and  Upper  (late) 
Cambrian  time.  (Slightly  modified  after  Bailey  Willis,  courtesy  of  The 
Journal  of  Geology.) 


THE  CAMBRIAN  PERIOD  67 

between  the  Upper  Cambrian  and  the  succeeding  Ordovician. 
Thus  we  know  that  the  Cambrian  period  closed  quietly.  As  above 
outlined,  the  one  great  physical  event  of  the  Cambrian  was  the 
gradual  submergence  of  large  portions  of  the  continent. 


CRENVILUC.  POTSBAM,  JHCRCSA  DRIFT 


Fig.  31 

Structure  section  in  Saratoga  County,  New  York,  showing  how  Upper  Cam- 
brian strata  overlap  upon  a  hillock  of  pre-Cambrian  rock  (Grenville). 
(After  W.  J.  MiUer,  N.  Y.  State  Mus.  Bui.  153.) 

The  failure  of  any  important  stratigraphic  break  (uncon- 
formity) between  the  Cambrian  and  Ordovician  systems  has 
forced  a  rather  arbitrary  separation  of  these  two  systems,  based 
almost  wholly  upon  important  changes  in  organisms. 

FOREIGN  CAMBRIAN 

Europe.  —  Like  that  of  North  America,  the  Cambrian  rocks 
of  Europe  generally  rest  upon  the  profoundly  eroded  surface  of 
either  Algonkian  or  Archean  rocks.  The  physical  geography  of 
the  continent,  however,  differed  considerably  because  the  dis- 
tribution of  the  rocks  shows  that  the  early  Cambrian  sea  was  almost 
wholly  limited  to  northern  Europe,  while  the  middle  Cambrian 
sea  transgressed  farthest  over  much  of  France,  Germany,  Bohemia, 
Spain,  and  Sardinia,  and  by  the  beginning  of  the  late  Cambrian 
the  sea  had  retrogressed  to  occupy  only  northern  Europe.  Thus 
much  of  Europe  did  not  become  progressively  submerged  like 
North  America. 

In  Wales  and  Brittany  the  Cambrian  strata  appear  to  have  a 
maximum  thickness  variously  estimated  at  from  12,000  to  20,000 
feet,  while  in  southern  Sweden  the  whole  Cambrian  is  only  about 
400  feet  thick.  Like  those  of  North  America,  the  rocks  are  mainly 
clastic  sediments  of  shallow  water  origin  such  as  conglomerates, 


68  HISTORICAL  GEOLOGY 

sandstones,  and  shales.  In  western  Europe,  for  example  in  Wales 
and  southern  Scandinavia,  the  Cambrian  strata  are  thoroughly 
indurated  and  usually  highly  folded,  but  in  eastern  and  central 
Europe,  for  example  in  Russia,  the  strata  are  mostly  practically 
horizontal,  and  even  unconsolidated  beds  of  sand  and  clay  have 
been  found.  Unconsolidated  beds  of  so  great  age  are  truly 
remarkable. 

The  Cambrian  period  closed  in  Europe  without  any  important 
physical  disturbance. 

Other  Continents.  —  The  Cambrian  of  other  continents  has 
generally  not  been  well  studied,  but  rocks  of  this  age  are  known  in 
Australia,  Tasmania,  India,  China,  Korea,  Siberia,  and  Argentina. 
Only  slightly  folded  or  tilted  strata  of  Cambrian  age  up  to  20,000 
feet  thick  are  known  in  northern  China.  Glacial  deposits  in  China, 
Norway,  and  Australia  will  be  described  under  the  next  heading. 

CLIMATE 

Very  distinct  evidences  of  glaciation  are  known  in  the  earliest 
Cambrian  or  possibly  late  Algonkian  of  China,  Norway,  Australia, 
and  perhaps  also  South  Africa.  At  the  base  of  the  thick  section  of 
Cambrian  strata  in  China  "on  the  Yangtse  River,  31°  Lat.,  i.e. 
as  far  south  as  New  Orleans,  not  high  above  sea  level,  a  large  body 
of  glacial  material  (170  feet  thick)  was  discovered.  ...  It  demon- 
strates the  existence  of  glacial  conditions  in  a  very  low  latitude  in 
the  early  Paleozoic. "  1 

At  Lat.  70°  N.  in  Norway,  glacial  deposits  containing  clearly 
striated  pebbles  have  been  found  resting  upon  a  distinctly  smoothed 
and  striated  surface  of  hard  rock. 

In  southern  Australia  glacial  beds  of  similar  age  and  consider- 
able thickness  are  distinctly  folded  along  with  the  enclosing  strata. 

The  significance  of  these  earliest  Paleozoic  glacial  deposits  is 
difficult  to  exaggerate  in  considering  the  climate  of  the  time.  The 
old  idea,  based  upon  the  Laplacian  Nebular  hypothesis,  that  early 
Paleozoic  climate  was  notably  warmer,  moister,  and  richer  in 
carbon  dioxide  than  now,  is  directly  refuted  by  the  evidence  of 
glaciation.  Such  evidences  of  glaciation,  combined  with  the  char- 
acter and  distribution  of  the  organisms,  indicate  that  Cambrian 

1  B.  Willis:  Researches  in  China  (Vol.  2),  Published  by  Carnegie  Insti- 
tution of  Washington. 


THE  CAMBRIAN  PERIOD  69 

climate  was  not  essentially  different  from  that  of  comparatively 
recent  geologic  time,  but  that  climatic  conditions  were  much  more 
uniform  over  the  earth  than  now. 

ECONOMIC  PRODUCTS 

Cambrian  rocks/  such  as  the  Potsdam  sandstone  and  Little 
Falls  dolomite  in  New  York,  furnish  considerable  quantities  of 
building  stone  for  local  use. 

Roofing  and  other  slates  of  Cambrian  age  are  extensively  quar- 
ried in  Vermont  and  eastern  New  York.  Also  the  famous  slate 
quarries  of  Wales  are  in  rocks  of  this  age. 

No  very  important  metalliferous  deposits  are  known  in  Cam- 
brian rocks. 

LIFE  OF  THE  CAMBRIAN 

Stage  of  Evolution  of  Cambrian  Life.  —  The  life  of  the  Cam- 
brian possesses  a  particular  importance  because,  excepting  the 
few  scant  organic  remains  found  in  upper  Algonkian  rocks,  the 
rocks_of  this  age  contain  the  oldest  known  assemblage  of  distinct 
fossils^Manylumdreds  of  Uambrian  species  have  been  described. 
.hJven  liere,  however,  the  organic  record  is  very  incomplete  both 
because  many  Cambrian  fossils  have  not  yet  been  discovered  and 
because  a  vast  number  of  Cambrian  organisms  must  never  have 
been  preserved  as  fossils.  Although  Cambrian  fossils  are  scant  as 
compared  with  those  of  other  Paleozoic  systems,  nevertheless  a 
striking  fact  is  the  large  number  and  complexity  of  organisms 
represented.  All  of  the  sub-kingdoms  of  invertebrate  animals  j 
are  represented,  though  nearly  always  by  only  the  simpler  types  | 
of  each  sub-kingdom,  and  this  together  with  the  positive  evidences 
for  pre-Cambrian  life,  make  it  perfectly  evident  that  organisms 
existed  and  developed  (evolved)  for  a  vast  length  of  time  before 
the  opening  of  the  Cambrian.  It  is  generally  agreed  that  fully 
half  of  the  evolution  of  organisms  had  taken  place  before  the 
beginning  of  the  Cambrian  period. 

In  spite  of  so  much  pre-Cambrian  evolution  of  organisms,  it  is 
to  be  remembered  that,  as  a  result  of  post-Cambrian  evolution, 
literally  enormous  advancement  has  been  made,  so  that  Cambrian 
forms  are  really  simple  or  primitive  as  compared  with  many  of  the 
highest  living  forms.  To  illustrate,  there  is  a  vast  gulf  between 
the  degree  of  organization  of  the  highest  Mammals  of  today  and 


70  HISTORICAL  GEOLOGY 

the  highest  forms  (simple  Arthropods)  of  Cambrian  time,  and 
all  of  this  development  has  been  gradually  accomplished  since 
Cambrian  time. 

Passing  upward  in  the  Cambrian  system,  the  fauna  shows  a 
gradual  progress  toward  more  highly  developed  or  organized  forms. 

Apparent  Suddenness  of  Appearance  of  the  Cambrian  Forms. 
-  The  apparent  suddenness  of  appearance  of  so  many  highly  devel- 
oped organisms  even  in  the  early  Cambrian  has  caused  much  dis- 
cussion by  way  of  attempted  explanation.  Geologists  are  agreed 
that  this  seeming  sudden  appearance  of  so  many  forms  is  due  to 
imperfection  of  the  record  either  because  of  unfavorable  conditions 
for  the  preservation  of  fossils  in  the  pre-Cambrian  sediments,  or 
because  fossils,  though  once  present  in  those  rocks,  have  been" 
obliterated  "by  subsequent  changes  or  metamorphism.  Further, 
it  is  agreed  that  the  first  organisms  were  plants  because  animal 
life  is  ultimately  dependent  upon  vegetable  matter  as  a  food 
supply. 

It  should  be  recognized  that  the  metamorphic,  or  crystalline, 
character  of  all  Archean  and  most  AJgonkian  rocks  is  obviously 
unfavorable  for  preservation  of  determmable  fossils.  Thus, 
Archean  sedimentary  rocks  have  flakes  of  graphite  (carbon)  dis- 
seminated through  them  and,  though  SJIG&--  carbon  is  of  organic 
origin,  the  priginal  organic  structures  h^ve/been  entirely  obliterated 
so  that  crysTallTzed  carbon  only  remains  after  the  intense  meta- 
morphism. Such  an  explanation,  h(weyer,  does  not  by  any  means 
answer  the  whole  question,  because,  /at  a  number  of  localities, 
thousands  of  feet  of  non-metamorphosed  pre-Cambrian  strata  are 
known  and,  except  in  very  few  cases  in  the  later  of  these  rocks, 
distinct  fossil  forms  are  not  known. 

Brooks  l  has  advanced  the  hypothesis  that  the  early  living 
forms  fplfl.nts  and  animals)  were  single  celled,  and  that  they 
originateoand  lived  in  the  surface  portions  of  the  ocean.  Because 
of  the  lack  of  severe  struggle  for  existence  in  such  environment, 
pelagic  (free-swimming)  plants  have  to  this  day  remained  largely 
primitive  or  single  celled.  For  similar  reasons  the  unicellular 
animals  long  failed  to  evolve  higher  forms  because  of  easy  existence 
in  contact  with  much  food  and  sunlight.  Such  forms  were  of  ge- 
latinous consistence  and  not  favorable  for  preservation  as  fossils. 
Not  until  the  attachment  to  the  bottom  or  along  shore  were  con- 
1  W.  K.  Brooks:  Jour.  GeoL,  Vol.  2,  1894. 


THE  CAMBRIAN  PERIOD  71 

ditions  favorable  for  the  development  of  higher  forms  by  the 
aggregation  of  cells.  The  plants  first  spread  to  the  shore  waters 
and  thence  over  the  land,  so  that  gradually  the  shore  waters  became 
clearer  and  richer  in  organic  material  and  hence  more  suitable 
habitats  for  animals.  The  animals  once  established  along  shore, 
about  the  beginning  of  the  Cambrian  or  late  in  the  pre-Cambrian, 
are  conceived  to  have  made  rapid  progress  in  evolution  because 
the  struggle  for  existence  became  severe  on  account  of  greater 
crowding  in  this  more  restricted  environment.  Support  became 
necessary  as  well  as  means  of  defense,  therefore  hard  parts  were 
developed,  and  such  hard  parts  could  be  preserved  as  fossils.  In 
harmony  with  this  hypothesis  is  the  important  fact  that  pre- 
Cambrian  and  early  Cambrian  fossil  shells  are  mostly  very  thin., 
heavy  shells  apparently  not  having  been  evolved  till  later. 

Another  hypothesis  "  assumes  that  the  first  forms  of  life  were 
simple  plants  that  originated  in  the  land  waters.  .  .  .  This  hy- 
pothesis further  assumes  that  the  early  animals,  to  a  greater  or 
less  degree,  had  their  origin  in  the  same  waters,  and  like  the  plants 
on  which  they  were  dependent  spread  thence  to  the  sea  and  out 
upon  the  land.  It  is  assumed  that  there  might  be  considerable 
development  of  aquatic  forms  of  animal  life  ...  in  the  land  waters 
before  they  became  denizens  of  the  seas,  and  their  appearance 
in  the  latter  might  be  at  some  rather  advanced  stage  of  their- 
evolution  and  hence  be  seemingly  sudden. "  1 

Plants.  —  There  are  certain  rather  obscure  impressions  and 
other  more  distinct  cluster-like  forms  which  may  be  sea-weeds, 
but  their  identification  is  not  at  all  positive.  As  stated  above, 
simple  plants  at  least  must  have  been  abundant  since  animals 
ultimately  depend  upon  plants  for  food.  Their  ^rarnity  QCL 
fossils  is  doubtless  due  to  the  unfavorable  character  of  the  simple 
(soft)  marine  plants  for  fossilization. 

Recently  certain  problematical  Cambrian  fossils,  long  known 
by  the  name  "Cryptozoon,"  have  been  determined  as  AJffpfr  by 
Walcott.  They  secreted  concentric  layers  of  carbonate  of  lime 
and  lived  in  water.  In  some  localities,  as  near  Saratoga  Springs, 
New  York,  distinct  beds  or  " reefs"  of  such  Algae  occur  in  lime- 
stone (see  Fig.  32). 

Protozoans.  — jFomminifers  have  been  found  even  in  Lower 
Cambrian  rocks.   "Triese  forms  are  very  much  like  the  modern 
1  Chamberlin  and  Salisbury:  Geology,  Vol.  2,  p.  302, 


72 


HISTORICAL  GEOLOGY 


marine  forms,  and  it  is  an  interesting  and  important  fact  that  such 
very  simple  types  have  persisted  throughout  all  of  geologic  time 
from  the  Cambrian  to  the  present,  while  profound  evolutionary 
changes  were  taking  place  in  the  animal  kingdom.  Radiolarians 
are  not  known  as  fossils.  Many  Protozoans  doubtless  existed,  but 
very  few  secreted  shells,  and  hence  not  many  species  could  have 
been  preserved  as  fossils. 


Fig.  32 

Calcareous  Algae,  Cryptozoon  proliferum,  forming  a  reef 
in  Upper  Cambrian  limestone  near  Saratoga  Springs, 
New  York.  (After  H.  P.  Gushing,  N.  Y .  State  Mus. 
Bui.  169.} 

Porifers.  —  True  Sponges  (Fig.  33)  were  fairly  abundant 
throughout  the  period,  their  siliceous  spicules  being  especially 
common  as  fossils. 

Coelenterates.  —  Hydrozoans  were  represented  by  both  the 
so-called  "Jelly-fishes"  and  the  Graptolites.  The  finding  of  many 
recognizable  casts  and  impressions  of  Jelly-fishes  (Fig.  34),  which 
consist  wholly  of  soft  parts,  is  a  remarkable  freak  of  fossil  preser- 
vation. Grq/ptQUtes,(Fig.  49)  were  common,  especially  in  the  later 
Cambrian.  These  were  slender,  plume-like,  delicate  forms  consist- 
ing of  colonies  of  cells.  They  were  pelagic  or  free  to  float  in  the 
open  sea.  One  genus  of  Graptolites,  confined  to  a  horizon  near 


THE  CAMBRIAN  PERIOD 


73 


the  summit  of  the  Cambrian,  is  well-nigh  world-wide  in  its  distri- 
bution and  beautifully  illustrates  the  importance  of  such  forms 


A  B 

Fig.  34 

A  Cambrian  Jelly-fish,  Brooksella  alternata.  (After 
Walcott,  from  Shimer's  "Introduction  to  the  Study 
of  Fossils,"  permission  of  The  Macmillan  Company.) 


Fig.  33 

A  Cambrian 
Sponge,  Lep- 
tomitus  zilteli. 
(After  Wal- 
cott.) 


for  purposes  of  correlation  over  wide  areas.  It 
should  be  stated  that  Graptolites  occur  only 
in  the  older  Paleozoic  strata. 

Anthozoans  (Corals)  were 
more  doubtfully  present  be- 
cause the  fossil  forms  so  greatly  resemble 
Sponges  (Fig.  35),  but  recent  study  seems  to 
indicate  that  some  at  least  were  true  Corals. 
Locally  such  coral-like  forms  were  common 
enough  to  form  reefs. 

Echinoderms.  —  Of  the  Echinoderms  the 
very  simplest  class,  called  Cystoids,  are  known 
to  have  existed.  These  were  the  bladder-like 
forms,  sometimes  with  rudimentary  arms,  set 
on  segmented  stems.  Holothuroids  ("sea  cu- 
cumbers") have  been  found  in  the  Cambrian 
of  British  Columbia  but  these  are  of  no  special 
Fig.  35  geologic  importance. 

A  Cambrian  Sponge          Worms.  —  Tracks  and  borings  of   marine 
or  Coral,  Archeo-     ^orms  are  COmmon,  but  no  actual  remains  are 
cyathus    rensse- 
laericus.     (After     known. 
Walcott.)  Molluscoids.  —  Brachiopods,  next  after  the 


74 


HISTORICAL  GEOLOGY 


a  Fig.  36  b 

Cambrian  Brachiopods :    a,  Lingulella  prima; 
b,  Lingulella  acuminata.     (After  Walcott.) 


Trilobites  (Crustaceans),  are  the  most  important  Cambrian  fossils 
(Fig.  36).  There  are  two  important  general  groups  of  Brachio- 
pods, namely,  the  Inar- 
ticulates, in  which  the 
horny  shells  or  valves  are 
not  joined  together  by  a 
hinge,  and  the  Articu- 
lates, in  which  the  heav- 
ier calcareous  shells  are 
joined  together  by  a  hinge 
structure.  The  former  are 
simpler  and'  lower  in  or- 
ganization, and,  from  the 
standpoint  of  evolution, 
it  is  important  to  note 

that  the  Cambrian  (and  also  pre-Cambrian)  Brachiopods  were 
mostly  Inarticulates,  the  Articulates  not  becoming  common  till 
in  the  Upper  Cambrian. 
In  the  post-Cambrian 
periods  the  Articulates 
greatly  outnumbered  the 
Inarticulates,  and  they 
are  the  most  common  of 
all  fossil  shells  in  the 
Paleozoic  rocks.  The  A  Cambrian  pelecypod  (Fordilla  troyensis). 
-r,  ,  .  ,  ,  Shell  on  right  and  cast  on  left,  much  en- 

Brachiopods    stand    out        larged     (After  Walcott.) 
conspicuously    as    a    re- 
markably persistent  class  of  animals  ranging  from  pre-Cambrian 
time  to  the  present,  and,  although  there  have  been  very  many 

species  and  genera  changes, 
the  class  as  such  has  been  very 
little  changed.  Many  hun- 
dreds of  species  are  known 
from  the  Paleozoic  rocks  alone, 
and  by  studying  their  gradual 
changes  in  species  and  genera, 

"  .     00          ,  they  have  come  to  rank  among 

a          Fig.  38          b  J  & 

~     ,  .       ~                        K/T  4i,     a  the  most   valuable  fossils    as 

Cambrian   Gastropods:  a,   Matherella  . 

saratogensis;    6,   Pelagiella  minutis-     geologic  time  markers  and  for 
sima.    (After  Walcott.)  purposes  of  correlation. 


37 


THE  CAMBRIAN  PERIOD 


75 


Mollusks.  —  All  the  principal  fossil-forming  types  of  Mollusks 
were  represented.  Pelecypod  shells  are  small  and  comparatively) 
rare,  being  mostly  found  in  the  Lower  Cambrian  (Fig.  37).  From 
Cambrian  time  to  the  present  they  have  steadily  increased,  both  as 
regards  number  of  species  and  individuals.  In  later  geologic  times 
the  shells  often  attained  great  size.  Gastropods,  mostly  of  simple, 
low-conical  types,  were  fairly  common  throughout  the  period 
(Fig.  38).  Cephalopods  comprise  the  highest  class  of  Mollusks 


Fig.  39 

Cambrian  Trilobites,  restored  forms :  a,  Olenellus  gilberti,  characteristic  of  the 
Lower  Cambrian;  6,  Paradoxides  bohemicus,  characteristic  of  the  Middle 
Cambrian;  c,  Dikellocephalus  pepinensis,  characteristic  of  the  Upper  Cam- 
brian. (From  Chamberlin  and  Sab'sbury's  "Geology,"  permission  of  Henry 
Holt  and  Company.) 

and  they  have  been  rarely  found  only  in  Middle  Upper  Cambrian 
strata.  They  were  simple,  straight,  or  curved,  chambered-shelled 
forms.  The  Cephalopods  became  very  important  in  subsequent 
periods,  and  the  evolution  of  the  class  will  be  dwelt  upon  in  suc- 
ceeding chapters. 

Arthropods.  —  Among  the  Arthropods  the  simpler  forms 
(Crustaceans)  only  are  known  from  the  Cambrian.  Trilobites  are 
by  far  the  most  abundant  and  significant  Cambrian  Arthropods 
(Figs.  39-40).  In  fact  they  are  the  most  important  Cambrian  fos- 
sils. We  have  seen  that  the  threefold  subdivision  of  the  Cambrian 
system  is  based  upon  the  changes  in  the  Trilobite  fauna.  Examples 
of  the  most  characteristic  Cambrian  genera  are  shown  in  Fig.  39. 


76 


HISTORICAL  GEOLOGY 


They  were  inhabitants  of  the  sea  and  they  were  the  most  highly 
organized  animals  of  the  time.  Trilobites  persisted  only  till  the 
close  of  the  Paleozoic  era,  and  were  especially  numerous  in  the 
earlier  periods  of  that  era.  The  name  Trilobite  refers  to  the  three- 
lobed  character  of  the  body.  The  creature  possessed  a  distinct 
with  compound  eyes,  and  a  more  or  less  distinct  _tail- 
sJiiejd.  Between  the  shields  there 
was  a  highly  segmented  body  por- 
tion. They  \ranged  in  length  from 
an  inch  or  less  to  about  two  feet. 
"The  Trilobites  display  an  extraor- 
dinary variety  in  form  and  size, 
in  the  proportion  of  the  head-and- 
tail-shields,  in  the  number  of  free 
segments,  and  in  the  development 
ofjspiues.  Already  in  the  Cambrian 
this  wealth  of  forms  is  notable, 
though  far  less  than  it  became  in 
the  Ordovician.  As  compared  with 
those  of  later  times,  the  Cambrian 
Trilobites  are  marked  by  the  (usu- 
ally) very  small  size  of  the  tail-shield, 
the  large  number  of  free  segments, 
and  their  inability  to  roll  them- 
selves up." l  Eucrustaceans  of  rather 
simple  types  (e.g.  Ostracods)  were 
present,  but  not  important. 

Arachnids  (e.g.  Eurypterids)  are  only  sparingly  known  from 
the  Cambrian.  These  forms  will  be  discussed  beyond. 

No  Known  Land  Animals  or  Vertebrates.  —  Thus  far  no 
fossil  land  animals  of  any  kind  have  been  found,  but  this  by  no 
means  proves  their  non-existence  during  the  Cambrian.  Ver- 
tebrates are  entirely  unknown,  and  if  any  existed  in  the  Cambrian 
we  know,  from  our  study  of  Vertebrates  of  succeeding  periods, 
that  they  must  have  been  of  the  very  simplest  types.  It  is  exceed- 
ingly doubtful  if  any  existed. 

1  W.  B.  Scott:  An  Introduction  to  Geology,  2nd  Ed.,  p.  556. 


Fig.  40 

A  Middle  Cambrian  Trilobite, 
Neolemus  serratus,  with  well 
preserved  appendages.  (After 
Walcott.) 


CHAPTER  VII 


THE    ORDOVICIAN    (LOWER    SILURIAN)    PERIOD 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

IN  the  preceding  chapter  we  learned  how  the  basal  portion  of 
Murchison's  great  Silurian  system  came  to  be  called  the  Cambrian. 
In  1879  Lapworth  proposed  to  divide  the  remaining  Silurian  system 
into  two  parts,  the  lower  portion  to  be  called  Ordovician,  and  the 
upper  to  retain  the  name  Silurian.  The  term  Ordovician  was  taken 
from  an  old  tribe  (Ordovici)  which  once  inhabited  Wales.  When 
it  is  realized  that  one  of  the  most  profound  stratigraphic  breaks 
(unconformities)  in  the  whole  Paleozoic  group  lies  within  Murchi- 
son's old  Silurian  system,  and  between  what  are  now  called  the 
Ordovician  and  Silurian  systems,  the  justification  of  Lapworth's 
proposal  is  evident.  In  America  and  England  the  Ordovician 
system  is  now  generally  recognized,  though  on  the  continent  of 
Europe  the  term  Lower  Silurian  is  still  largely  employed  instead. 
The  following  tabular  arrangement  will  serve  to  make  clear  the 
history  of  these  terms : 


(Murchison,  1835} 

(Sedgwick) 

(Lapworth,  1879} 

{  Upper  Silurian 

Silurian  system  {  T           0.,     . 
1  Lower  Silurian 

Upper  Silurian 
f  Lower  Silurian 
\  Cambrian 

Silurian 
Ordovician 
Cambrian 

Since  the  North  American  Ordovician  was  first  carefully  studied 
in  New  York  state,  the  section  there  has  become,  to  a  very  consid- 
erable degree,  the  standard  to  which  the  subdivisions  in  other 
parts  of  the  continent  are  referred.  During  recent  years  several 
unconformities,  though  rather  minor  ones,  have  been  discovered 
in  the  New  York  Ordovician,  so  that  this  section  is  not  as  perfect 
or  continuous  (stratigraphically)  as  was  formerly  supposed,  certain 
records  being  entirely  missing.  Following  are  the  principal  sub- 
divisions of  the  New  York  Ordovician  system  according  to  the 
most  recent  classification  by  the  State  Geological  Survey : 

77 


78  HISTORICAL  GEOLOGY 


,.  (  Lorraine  shale  and  sandsk 
CINCINNATI  AN  SERIES   j  Frankfort.  I 

(Upper  Ordovician)    [  Utica  shale. 

MOHAWKIAN  SERIES      /  Trenton  limestone  and  shale. 
(Middle  Ordovician)  \  Black  River  limestone. 


CANADIAN  SERIES 
(Lower  Ordovician) 


Chazy  limestone. 
Pamelia  limestone. 
Beekmantown  limestone. 
Tribes  Hill  limestone. 


The  reader  should  not  be  led  to  think  that  these  New  York 
formation  or  stage  names  are  the  only  ones  now  used  in  North 
America.  Many  other,  more  or  less  local,  names  have  been  applied 
either  to  formations  (stages)  found  elsewhere  but  missing  in  New 
York,  or  to  formations  which  have  not  yet  been  definitely  cor- 
related with  those  of  New  York.  It  is  generally  agreed,  on  the  basis 
of  priority,  that  when  two  widely  separated  formations  become 
definitely  correlated,  the  name  given  the  formation  where  first 
studied  is  to  be  applied  to  both.  In  this  way  many  of  the  New 
York  names  have  come  to  be  used  over  wider  and  wider  areas. 
Also  the  kind  of  rock  (lithologic  character)  making  up  a  formation 
in  New  York  may  or  may  not  be  the  same  in  other  areas.  Thus  a 
sandstone  or  shale  in  New  York  may  be  replaced  by  a  shale  or 
limestone  elsewhere,  etc. 

In  New  York,  and  usually  elsewhere,  the  Ordovician  strata, 
especially  the  Middle  and  Upper,  and  more  especially  the  Trenton 
beds,  are  wonderfully  rich  in  organic  remains,  and  much  attention 
has  been  given  to  the  description  of  the  fossils  and  the  correlation 
of  the  strata.  Unconformities  within  the  Ordovician  system  are 
relatively  uncommon,  those  which  do  occur  seldom  ever  being  of 
more  than  local  extent.  In  other  words,  with  certain  slight  ex- 
ceptions, deposition  of  Ordovician  strata  in  North  America  was  a 
continuous  process,  and  the  subdivisions  are  very  largely  on  the 
basis  of  fossils. 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  The  accompanying  map  (Fig.  41) 
shows  the  distribution  of  chiefly  Middle  and  Upper  Ordovician 
rocks  in  North  America.  Some  Lower  Ordovician  rocks  are  in- 
cluded with  the  Cambrian  on  the  preceding  map  (Fig.  26),  but 


THE  ORDOVICIAN  PERIOD 


79 


1  Lower  Ordovician  rarely  occurs  in  any  areas  not  also  occupied 
the  Middle  Ordovician,  the  accompanying  map  shows  the 
e  distribution  of  practically  all  Ordovician  strata.    By  com- 
ing the  maps  (Figs.  26  and  41)  it  will  be  seen  that  the  distri- 


Fig.  41 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  chiefly  Middle 
and  Upper  Ordovician  strata  in  North  America.  (By  W.  J.  M.,  based  upon 
maps  by  Bailey  Willis,  U.  S.  Geological  Survey.) 

bution  of  Ordovician  rocks  is  essentially  the  same  as  that  of  Upper 
Cambrian,  with  two  important  differences.  These  differences  are 
the  presence  of  two  large  areas  of  Ordovician  west  of  Hudson  Bay, 
and  a  number  of  smaller  areas  in  the  Arctic  Islands  region. 

As  in  the  case  of  the  Cambrian,  so  the  surface  distribution  of 


THE  ORDOVICIAN  PERIOD  81 

the  Ordivician  rocks  as  indicated  on  this  map  gives  no  adequate 
idea  of  the  former  or  present  real  extent  of  strata  of  this  age,  since 
strata  have  either  been  removed  from  so  many  districts  by  erosion, 
or  are  concealed  under  later  formations,  or  are  highly  folded 
so  that  outcropping  edges  only  are  at  present  visible.  Some  regions 
can  quite  certainly  be  shown  to  have  been  formerly  covered  by 
Ordovician  strata,  as,  for  instance,  nearly  all  of  the  Adirondack 
Mountain  region,  and  a  wide  belt  between  the  Great  Lakes  and 


Fig.  43 

The  Trenton  (mid-Ordovician)  limestone  at  its  type  locality,  Trenton  Falls, 
New  York.     (Photo  by  F.  B.  Guth,  Utica,  N.  Y.) 

Hudson  Bay.  Also  the  distribution  of  outcrops,  together  with  nu- 
merous deep-well  sections,  conclusively  prove  that  much,  if  not  all, 
of  the  Mississippi  Basin  contains  concealed  Ordovician  rocks.  In 
the  Appalachians,  New  England,  and  some  of  the  western  moun- 
tains extensive  Ordovician  strata  are  actually  exposed  only  along 
comparatively  narrow  belts  following  the  strike  of  the  highly 
folded  rocks. 

Lower  and  Middle  Ordovician  Rocks.  —  Viewed  in  a  broad 
way,  the  Ordovician  rocks  (especially  the  Lower  and  Middle)  are 


82  HISTORICAL  GEOLOGY 

of  quite  different  character  from  those  of  the  Cambrian.  Clastic 
sediments,  such  as  conglomerates,  sandstones,  and  shales,  were  the 
dominant  Cambrian  sediments,  while,  throughout  the  Lower  and 
Middle  Ordovician,  limestones  greatly  predominate  (Fig.  44). 
Mid-Ordovician  is  generally  regarded  as  one  of  the  greatest  lime- 
stone making  times  in  the  earth's  history,  though  it  should  not  be 
inferred  that  limestones  were  then  universally  made  in  the  seas, 
because  those  areas  of  deposition  close  to,  or  receiving  wash  from, 
the  lands  show  clastic  sediments.  Middle  Ordovician,  especially 
Trenton,  limestones  are  remarkably  widespread,  occurring  in  New 
York,  New  England,  New  Brunswick,  southeastern  Canada,  and 
near  Hudson  Bay,  across  the  northern  part  of  the  Mississippi 
Basin,  Black  Hills,  Wasatch  and  Uinta  Mountains,  and  even  in 
the  Great  Basin.  An  illustration  of  an  exception  to  universal 
limestone-making  during  Trenton  time  is  in  the  Mohawk  Valley 
region  of  New  York,  where  the  limestone  passing  eastward  be- 
comes almost  wholly  replaced  by  hundreds  of  feet  of  shale.  Also 
through  the  Appalachians  rocks  of  this  age  contain  much  clastic 
material. 

Upper  Ordovician  Rocks.  —  In  the  Upper  Ordovician  of  eastern 
North  America  shales  and  alternating  shales  and  fine-grained  sand- 
stones (e.g.  Utica  and  Lorraine)  greatly  predominate,  doubtless 
due  to  rejuvenation  and  more  active  erosion  of  the  lands  probably 
accompanied  by  some  shoaling  of  the  water  (Fig.  44) .  In  the  west- 
ern part  of  the  continent  limestones  appear  to  predominate,  even 
in  the  Upper  Ordovician. 

Thickness  and  Metamorphism  of  the  Ordovician.  —  The 
aggregate  thickness  of  Ordovician  strata  in  New  York  is  from  2000 
to  3000  feet;  in  Tennessee  about  4000  feet;  and  in  the  central 
Mississippi  Valley  (e.g.  Missouri)  only  a  few  hundred  feet. 

Among  the  changes  which  the  strata  have  undergone  since  their 
deposition  we  have  mentioned  their  highly  folded  condition  in 
certain  regions,  but  in  New  England,  parts  of  the  Piedmont 
Plateau,  and  parts  of  the  western  United  States  the  rocks  are  also 
highly  metamorphosed. 

Igneous  Rocks.  —  There  is  no  certain  evidence  for  volcanic  or 
other  igneous  activity  during  the  North  American  Ordovician, 
though  some  granite  intrusions  in  the  Wichita  Mountains  of 
Oklahoma  and  some  very  small  dikes  in  New  York  may  be  of 
this  age. 


System 


Kind  of  Rock 


shaly 
sandstone 


sandstone 


shale 


sandstone 


shale 


limestone 


dolomitic 
limestone 


shale 


limestone 


shale 


limestone 


Section 


Thickness 
in  feet 


700+ 


350 

to 

900 


1300 

to 
1800 


2-200 


1000+ 


450 
to 
950 


3000 

to 
3500 


500 
to 
750 


700 

to 

950 


200 


400+ 


o  oo 


1* 

03    £ 

I 


0° 


13 

e  S3 
13 


II 

^O 

o  t, 
^3    8 

Jl 


P 

~ 


. 

VI 


11 


2 

bfi 
O 

o 

m 

O 


84  HISTORICAL  GEOLOGY 


PHYSICAL  HISTORY 

Early  and  Middle  Ordovician.  —  The  progressive  submergence l 
which  caused  so  much  of  North  America  to  be  covered  by  marine 
waters  by  late  Cambrian  time  continued  well  into  the  Ordovi- 
cian, so  that  during  mid-Ordovician  time  more  of  the  continent 
appears  to  have  been  covered  by  the  sea  than  at  any  other  time  in 
its  history  since  the  beginning  of  the  Paleozoic  era.  A  good  idea 
of  the  general  relations  of  land  and  sea  at  this  time  may  be  gained 
from  the  paleogeographic  map  (Fig.  45) .  The  principal  land  areas 
were  Appalachia  (except  the  Piedmont  Plateau  district  in  the  early 
Ordovician)  along  the  Atlantic  Coast;  the  Labrador  region;  Lake 
Superior  and  southward;  west  of  Hudson  Bay;  Wyoming  to 
Arizona;  Ozark  Mountains  of  Missouri;  and  certain  rather  in- 
definitely known  and  possibly  connected  areas  to  the  west  of  the 
Rocky  Mountains. 

Because  Ordovician  strata  often  show  a  thickness  of  2000  to 
4000  feet,  it  should  not  be  inferred  that  the  Ordovician  sea  was 
necessarily  ever  2000  to  4000  feet  deep.  Even  the  limestones 
often  abundantly  prove  by  ripple-marks,  mud-cracks,  fossils, 
etc.,  that  they  were  laid  down  in  shallow  water.  The  very  char- 
acter of  the  thickest  materials  (old  muds  and  sands)  in  the  Upper 
Ordovician  implies  that  they  could  not  have  been  deposited  in 
deep  ocean  water.  Such  sediments  are  not  now  forming  on  the 
deep  sea  bottom.  But  how  are  these  statements  to  be  harmonized 
with  the  fact  that  Ordovician  strata  several  thousand  feet  thick 
actually  exist  over  considerable  areas?  During  the  early  and  middle 
portions  of  the  period  (with  certain  rather  local  exceptions  above 
mentioned)  the  land  gradually  became  submerged,  and  stratum 
after  stratum  was  formed  upon  the  relatively  sinking  sea  floor 
(or  submerging  land),  so  that  at  no  time  is  it  necessary  to  assume 
great  depth  of  water.  In  general,  the  early  to  middle  Ordovician 
sea  of  North  America  must  be  thought  of  as  a  vast  shallow 
(epicontinental)  ocean  which  spread  over  most  of  the  slowly  sub- 
merging continent.  There  were  no  ocean  abysses  at  all  comparable 
to  those  of  the  present  Atlantic  or  Pacific. 

1  This  disregards  the  probable  temporary  withdrawal  of  the  late  Cam- 
brian sea  from  the  upper  Mississippi  Valley  region  as  explained  in  the 
preceding  chapter. 


MIDDLE  ORDOVICIAN 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAI.) 
SEA  OR  LAND,  MORE  LIKELY  SEA 
LAND  OR  SEA,  MORE  LIKELY  LAND 
LANDS 

tNDETERMINATE  AREAS 
MARINE  CURRENTS 


Fig.  45 

Paleogeographic   map   of  North   America  during   Middle  Ordovician  time. 
(Slightly  modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.) 


86  HISTORICAL  GEOLOGY 

Late  Ordovician.  —  Soon  after  Trenton  time  in  the  Wichita 
Mountain  district  of  Oklahoma  there  was  a  rather  local  crustal 
disturbance,  when  the  strata  were  upturned  and  granite  intrusions 
are  thought  to  have  taken  place. 

Since  the  later  Ordovician  sediments  are  mostly  clastic  (shales 
and  sandstones),  it  is  evident  that  an  important  change  in  the 
physical  geography  conditions  took  place  during  the  latter  portion 
of  the  period.  Considerable  areas  of  sea  bottom  were  gradually 
converted  into  dry  land,  and  other  portions  were  shoaled.  Either 
an  uplift  of  the  land,  or  a  withdrawal  of  epicontinental  sea  waters 
by  sinking  of  the  ocean  bottoms  (Atlantic  and  Pacific),  or  both 
may  have  produced  the  change.  The  newly  exposed  lands,  and 
the  relatively  higher  old  lands,  suffered  pretty  rapid  erosion,  and 
clastic  sediments  accumulated  comparatively  fast.  As  we  shall 
presently  see,  considerable  crustal  disturbances  (orogenic),  ac- 
panied  by  uplifts,  reached  their  climax  toward  the  close  of  the 
period  in  eastern  North  America,  and  there  is  much  evidence  to 
show  that  such  actual  uplifts  began  well  before  the  close  of  the 
period. 

Close  of  the  Ordovician  (Taconic  Revolution).  —  In  marked 
contrast  with  the  quiet  close  of  the  Cambrian,  the  Ordovician 
ended  with  important  physical  or  crustal  disturbances  and  moun- 
tain-making. Much  of  the  interior  (epicontinental)  sea  appears  to 
have  been  drained  as  a  result  of  relative  changes  in  level  between 
land  and  sea,  gradually  increasing  during  late  Ordovician  time. 
In  this  interior  region  the  land  was  mostly  but  slightly  elevated 
to  remain  dry  only  till  the  early  part  of  the  next  period. 

We  have  learned  that  sedimentation  was  practically  uninter- 
rupted during  the  Cambrian  and  Ordovician  periods,  and  that 
some  thousands  of  feet  of  strata  had  accumulated  in  the  seas  which 
covered  eastern  New  York,  all  of  the  regions  of  the  present  Berk- 
shire Hills,  Green  and  White  Mountains,  as  well  as  southward  at 
least  to  Virginia  and  over  the  region  occupied  by  the  present  Pied- 
mont Plateau.  Toward  the  close  of  the  Ordovician  period  a  great 
compressive  force  was  brought  to  bear  in  the  earth's  crust  upon 
the  mass  of  sediments  which  reached  from  New  England  to 
Virginia,  and  possibly  farther  southward.  As  a  result  of  this  com- 
pression the  strata  were  tilted,  highly  folded,  and  elevated  far 
above  sea  level  into  a  magnificent  mountain  range  which  has 
been  called  the  Taconic  Range,  and  this  great  physical,  (orogenic) 


THE  ORDOVICIAN  PERIOD 


87 


disturbance  has  been  called  the 
Tfl.nom>.    T?pyr)]iitinn      In    struc- 


ture, the  range  consisted  of  a 
series  of  folds,  both  great  and 
small,  whose  axes  were  parallel  to 
the  main  axis  of  the  range,  that  is 
north-northeast  by  south-south- 
west. Examination  of  Fig.  46 
will  give  the  reader  a  good  con- 
ception of  the  character  of  the 
folding.  It  is  quite  the  rule, 
throughout  this  region  of  Taconic 
disturbance,  to  find  the  strata 
either  on  edge  or  making  high 
angles  with  the  plane  of  the  hori- 
zon. Many  times  the  folds  were 
actually  overturned,  and  in  places 
notable  thrust  faults  were  de- 
veloped. These  facts  all  go  to 
prove  that  the  mountain-making 
compressive  force  applied  to  the 
»  region  was  of  rather  an  extreme 
type.  Though  we  have  no  way 
of  telling  just  how  high  the  range 
may  have  been,  nevertheless  the 
structural  features  and  the  vast 
amount  of  erosion  since  the  folds 
were  produced  clearly  indicate 
that  the  uplift  was  at  least  some 
thousands  of  feet.  The  Green  and 
White  Mountains,  Berkshire  Hills, 
Highlands  of  the  Hudson,  and  the 
Piedmont  Plateau  are,  in  a  sense, 
the  remnants  or  roots  of  the  great 
Taconic  Range. 

In  passing  westward  from  the 
main  axis  of  the  range,  the 
folding  is  less  and  less  intense, 
till  finally  the  folds  die  out  alto- 
gether. 


en 


O     GO     ft) 


GO  C       O 

ft1! 

u   i-i   rn 


W 


[  Crush  2 one 
Gneiss 


Crush  Zone 


S\  Granite 


iffrrefss  „ 

and  oromn 

*  Greatlbu/t 
\Qa//ou/s  Jfi/l 


Gmtss 


88  HISTORICAL  GEOLOGY 

How  do  we  know  that  the  Taconic  disturbance  took  place 
toward  the  close  of  the  Ordovician  period?  Strata  of  the  next 
succeeding  period  (Silurian)  rest  directly  in  places  upon  the  eroded 
edges  of  late  Ordovician  rocks;  hence  it  is  obvious  that  the  disturb- 
ance occurred  before  the  Silurian  strata  were  deposited.  Also  the 
disturbance  doubtless  began  before  the  close  of  the  Ordovician 
period.  This  is  borne  out  by  the  fact  that,  for  example,  in  central 
New  York  a  distinct  eroded  surface  at  the  summit  of  the  Frankfort 
shales  proves  that  region  to  have  been  dry  land  before  the  end  of 
the  period,  this  uplift  quite  certainly  having  been  produced  by  the 
early  movements  of  the  Taconic  disturbance. 

Another  feature  which  must  not  be  overlooked  is  the  profound 
metamorphism  of  the  strata  along  the  main  axis  of  the  Taconic 
Range.  The  very  intense  compression,  accompanied  by  heat  and 
moisture,  caused  the  deeply  buried  strata,  along  the  main  axis  of 
the  uplift,  to  become  rather  plastic,  and  hence  the  sediments  be- 
came more  or  less  foliated  and  crystallized  into  the  various  meta- 
morphic  rock  types,  the  limestone  becoming  marble,  the  shale 
becoming  slate  or  schist,  and  the  sandstone  becoming  quartzite. 

In  New  Brunswick,  Silurian  strata  rest  upon  the  eroded  edges 
of  upturned  Ordovician  strata,  and  this  upturning  may  have  been 
coincident  with  the  Taconic  disturbance. 

Sufficient  lateral  pressure  was  brought  to  bear  in  a  portion  of 
the  Mississippi  Basin,  during  the  latter  part  of  the  period,  to 
produce  a  long,  very  low  arch  in  the  rocks  from  southern  Ohio  into 
Tennessee.  This  has  been  called  the  "  Cincinnati  Anticline. " 

The  late  Cambrian  and  Ordovician  connection  of  the  interior 
sea  with  the  Atlantic  Ocean  through  the  St.  Lawrence  Valley  was 
closed  by  the  disturbances  toward  the  end  of  the  Ordovician. 


FOREIGN  ORDOVICIAN 

Map  Fig.  47  gives  a  general  idea  of  the  relations  of  land  and 
sea  in  Europe  during  the  Ordovician.  Also,  barring  certain  areas 
from  which  the  strata  have  been  removed  by  erosion,  the  dotted 
(shaded)  portion  represents  the  present  extent  (surface  and  con- 
cealed) of  Ordovician  strata.  There  were  two  distinct  provinces, 
a  northern  and  •  a  southern,  as  proved  by  important  differences 
between  the  fossils  of  northern  and  southern  Europe.  Ordovician 
fossils  of  northern  Europe  are  closely  related  to  those  of  North 


THE  ORDOVICIAN  PERIOD 


89 


America,  thus  implying  a  shallow  sea  connection  between  North 
America  and  Europe.  The  scarcity  of  limestone  in  the  European 
Ordovician  is  in  marked  contrast  with  that  of  North  America. 

In  the  British  Isles,  where  the  European  Ordovician  is  thickest 
(being  many  thousands  of  feet),  great  igneous  intrusions  and  ex- 
trusions took  place,  so  that  this  region  ranks  as  one  of  the  greatest 
ancient  volcanic  areas  in  Europe. 


Fig.  47 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe 
during  Ordovician  time.  Dotted  area,  water.  (Slightly  modi- 
fied after  De  Lapparent.) 

As  in  North  America,  important  geographic  changes  took  place 
toward  the  close  of  the  period,  and  the  Silurian  often  rests  by 
unconformit}-  upon  the  Ordovician.  In  the  British  Isles  the  Ordo- 
vician rocks  were  folded,  upraised,  and  often  metamorphosed,  with 
Silurian  strata  resting  upon  their  eroded  edges. 

Ordovician  rocks  are  also  known  in  Peru,  Argentina,  Australia, 
Tasmania,  New  Zealand,  Africa,  India,  eastern  China,  and  north- 
ern Siberia, 


90  HISTORICAL  GEOLOGY 

CLIMATE 

Red  sandstones,  salt,  and  gypsum  in  the  Upper  Ordovician  of 
northern  Siberia  clearly  imply  an  arid  climate  in  northern  Asia 
during  the  late  Ordovician.  So  far  as  can  be  determined  from  the 
character  of  the  rocks,  geographic  conditions,  and  distribution  of 
the  fossils,  the  climate  of  North  America  and  Europe  must  have 
been  mild  and  much  more  uniform  than  now.  Ordovician  fossils, 
even  from  Arctic  lands,  are  very  similar  to  those  of  low  latitudes. 

ECONOMIC  PRODUCTS 

Many  great  marble  quarries  are  located  in  metamorphosed 
Ordovician  limestone  in  New  England  and  the  Piedmont  Plateau. 
Also  much  non-metamorphosed  limestone  is  quarried  for  building 
purposes  or  burnt  for  lime  in  various  parts  of  the  United  States. 
In  the  Lehigh  district  of  Pennsylvania  much  Trenton  (argilla- 
ceous) limestone  is  used  in  the  manufacture  of  Portland  cement. 

Among  the  greatest  lead  and  zinc  ore  deposits  in  the  world  are 
those  of  the  Mississippi  Valley,  especially  in  Missouri,  Wisconsin, 
Iowa,  and  Illinois.  These  ores,  which  were  originally  disseminated 
through  the  limestones,  were  dissolved  and  redeposited  in  more 
concentrated  form  in  openings  in  the  rocks. 

Manganese  ores  of  Arkansas  and  phosphate  deposits  of  Ten- 
nessee occur  in  limestones  of  this  age. 

The  great  oil  and  gas  field  of  Ohio  and  Indiana  derives  its 
principal  supply  from  the  Ordovician  rocks,  especially  the  Tren- 
ton limestone.  The  oil  and  gas  were  formed  by  the  decomposition 
of  the  rich  organic  accumulations  in  the  limestones. 

LIFE  OF  THE  ORDOVICIAN 

Abundance  of  Marine  Life.  —  The  Ordovician  epicontinental 
seas  literally  swarmed  with  marine  organisms,  few  systems  contain- 
ing a  fuller  record  of  marine  forms  than  the  Ordovician  because  of 
very  favorable  conditions  of  fossilization.  As  regards  both  diver- 
sity and  abundance  of  known  organisms,  this  period  is  far  superior 
to  the  Cambrian.  Schuchert  states  that  over  1600  species  of 
animals  are  known  from  the  middle  Ordovician  alone.  It  is  to 
be  noted,  however,  that,  with  very  slight  exception,  VejJ£hEaie 
Lais  are  not  known  to  have  existed  in  the  Ordovician.  Also 


THE  ORDOVICIAN  PERIOD 


91 


our  knowledge  of_  land  plants  and  animals  is  very  son.nt.  The 
scarcity  of  land  organisms  may  have  been  due  to  prevalent  oceanic 
conditions  not  favorable  for  fossilization,  though  it  is  also  likely 
that  land  plants  and  animals  had  not  progressed  far  or  become 
very  abundant  so  early  in  the  history  of  the  earth.  Because  of 
the  unusual  abundance  and  diversity  of  invertebrate  animal  forms 
in  such  an  ancient  fossiliferous  system,  a  fuller  discussion  will  be 
devoted  to  these  forms  than  \ 

in  succeeding  chapters. 

Plants.  —  In  this  period, 
as  well  as  in  the  Cambrian, 
plant  life  of  very  simple 
types  at  least  must  have 
been  abundant  to  serve  as 
a  direct  or  indirect  food 
supply  for  the  myriads  of 
animals.  Various  fossil  sea- 
weeds (marine  Alga?)  are 
definitely  known,  especially 
in  the  Trenton  series  and 
younger  Ordovician  shales 
(Fig.  48).  The  rather  im- 
perfect record  is  doubtless 
due  to  the  fact  that  such  very  simple  forms  were  unfavorable  for 
fossilization.  Definite  knowledge  of  land  plants  is  lacking,  though 
a  few  rather  doubtful  higher  Cryptogams  are  said  to  have  been 
found  in  Europe.  In  view  of  the  abundant  land  flora  of  the  De- 
vonian, it  seems  more  than  probable  that  land  plants  existed  as 
early  as  the  Ordovician,  and  some  may  yet  be  discovered. 

Protozoans.  —  Both  Foraminifers  and  Radiolarians  must  have 
been  common  in  the  seas,  because  in  some  places  many  fossil  forms 
have  been  found.  As  in  the  preceding  period,  many  forms  without 
shells  almost  certainly  existed.  • 

Porif ers.  —  Sponges  were  more  abundant  and  diversified  than 
in  Cambrian  time,  and  some  were  of  large  size.-  Mostly  only  those 
Sponges  which  secreted  skeletons  were  favorable  for  fossilization. 

Coelenterates.  —  Hydrozoans  were  abundantly  represented  by 
the  Graytolites  (Fig.  49) ,  and  in  fact  the  Ordovician  may  be  said  to 
have  been  the  period  of  culmination  of  this  remarkable,  long 
extinct  group  of  animals.  They  are  so  abundant  and  varied  in 


Fig.  48 

Ordovician  Seaweeds,  Callithamnopsis  fruc- 
ticosa.     (After  Ruedemann). 


92 


HISTORICAL  GEOLOGY 


Upper  Ordovician  shales  that  definite  stages  or  horizons  have  been 
determined  largely  by  their  use.  Since  the  Graptolites  were  mostly 
floating  forms  and  widely  distributed  at  a  given  time,  they  have 
been  of  great  value  in  correlating  even  minor  subdivisions  of  the 
system  in  such  far  separated  regions  as  Great  Britain,  eastern 
North  America,  and  Australia.  When  it  is  further  stated  that  all 
known  Graptolites  are  confined  to  the  first  four  great  fossiliferous 
systems  (Cambrian,  Ordovician,  Silurian,  and  Devonian),1  their 
additional  importance  as  stratigraphic  indices  becomes  evident. 
In  Fig.  49  the  forms  represent  skeletons  or  axes  of  colonies,  a  single 


Fig.  49 

Ordovician  Graptolites:  a,  Tetragraptus  fructicosus;  b,  Climacograptus  bi- 
cornis;  c,  Diplograptus  pristis;  d,  Didymograptus  nitidus;  e,  Dictyonema 
flabelliforme.  (a,  b,  d}  after  Hall;  c,  after  Ruedemann;  e,  after  Matthew.) 

or  a  double  row  of  protoplasmic  cells  having  been  arranged  along 
an  axis.  Forms  with  cells  on  both  sides  of  the  axis  were  very  char- 
acteristic of  the  Ordovician. 

Anthozoans  (Corals)  were  common,  more  especially  where  the 
mid-Ordovician  limestones  were  forming.  It  will  serve  our  pur- 
pose to  divide  the  principal  Paleozoic  Corals  into  three  groups  or 
types  as  follows:  (1)  Cup  Corals  (solitary  or  compound),  (Fig. 
62a);  (2)  honeycomb  Corals  (compound),  (Fig.  62b);  and  (3)  chain 
Corals  (compound),  (Fig.  62c).  These  Paleozoic  Corals  were  all 
Tetracoralla,  that  is,  the  radiating  partitions  (septa)  of  the  indi- 
viduals or  polyps  were  four  in  number  or  multiples  of  four,  while 
modern  Corals,  which  first  appeared  in  the  Mesozoic  era,  are 
1  A  very  few  Graptolites  also  occur  in  the  Mississippian. 


THE   ORDOVICIAN  PERIOD  93 

Hexacoralla  or  Octacoralla.  Modern  Corals  are  nearly  all  pro- 
fusely branched  and  the  polyps  are  very  small,  while  Paleozoic 
Corals  were  rarely  branched  and  the  polyps  were  much  larger,  the 
cup  Corals  usually  ranging  from  half  an  inch  to  a  foot  or  more  in 
length.  All  three  types  of  Corals  above  mentioned  existed  in  the 
Ordovician,  but  solitary  cup  Corals  were  predominant.  Com- 
pound forms,  especially  honeycomb  Corals,  were  sometimes  locally 
abundant.  Among  modern  Corals  the  compound  or  colonizing 
forms  are  by  far  more  common  than  the  solitary  forms. 

Echinoderms.  —  All  the  classes  of  the  Echinoderms  were  re- 
presented in  the  Ordovician,  and  all  of  these  but  the  Cystoids  and 


a  b  c 

Fig.  50 

Ordovician  Echinoderms:  a,  Cystoid,  Pleurocystis  filitextus; 
b,  Crinoid,  Glyptocrinus  dyeri;  c,  Asterozoan,  Paleasterina 
stellata.  (a,  c,  after  Billings;  6,  after  Meek.) 

Holothuroids  made  their  first  appearance.  Cystoids  (Fig.  50a) 
reached  their  climax  of  development  in  this  period,  though  they 
did  not  become  extinct  till  the  Devonian.  Blastoids  were  rare 
and  represented  by  very  primitive  forms,  with  distinct  Cystoid 
affinities.  In  fact  the  Blastoids  assumed  little  importance  till  the 
Mississippian.  Crinoids  (Fig.  50b)  became  prominent,  and,  be- 
cause of  their  hard  parts,  were  well  suited  for  fossilization,  though, 
on  account  of  their  highly  segmented  character,  they  usually  fell 
apart  after  the  decay  of  the  soft  parts,  and  consequently  entire 
specimens  are  not  common.  Ophiuroids,  Asteroids  (Fig.  50c), 
and  Echinoids  were  uncommon,  the  latter  being  represented  by 
very  primitive  forms.  Holothuroids  are  not  known  as  fossils. 


94 


HISTORICAL  GEOLOGY 


Molluscoids.  —  Bryozoans  were  abundant  often  as  reef  builders, 
particularly  in  the  later  portion  of  the  period.  Hundreds  of  Ordo- 
vician  species  are  known.  Though  structurally  (organically)  very 
closely  related  to  the  Brachiopods,  they  are  far  different  from 
them  in  outward  appearance,  while  they  look  so  jnuchJike  the 

Corals  as  often  to  be  dis- 
tinguished from  them  with 
difficulty  (Fig.  51).  The 
Bryozoans  afford  a  fine 
illustration  of  a  class  of 
creatures  whose  genera 
have  changed  very  little 
from  very  ancient  times 
to  the  present  day. 

became 


much  more  abundajit, 
more  varied,  and  more 
complex  than  in  the  Cam- 
brian (Fig.  52).  Those 
with  hinged  shells  (Artic- 
ulates) greatly  outnum- 
bered the  Inarticulates 
for  the  first  time.  Also 
the  shells  usually  were 
thicker  and  more  difficult 
for  their  enemies  to  open 
because  of  long-hinged 
lines,  or  a  fluted  or  ribbed 
structure,  or  both.  As 
for  the  early  Paleozoic  in 
general,  nearly  all  were 

straight-hinged.  Many  genera  and  species  are  known,  certain  of 
them  having  been  much  used  in  subdividing  the  Ordovician  sys- 
tem. Along  with  the  Trilobites,  the  Brachiopods  were  the  most 
prominent  known  organisms  of  the  period.  About  300  species  are 
known  from  the  Middle  Ordovician  of  North  America  alone. 

Mollusks.  —  As  compared  with  the  Cambrian,  a  wonderful 
development  of  Mollusks,  both  as  regards  numbers  of  individuals 
and  species,  took  place  in  the  Ordovician. 

Pelecypod  bivalves  were  more  abundant,  usually  larger,  and  of 


Fig.  51 

Various  Ordovician  Bryozoans  on  a  slab  of 
limestone.  (After  R.  S.  Bassler,  U.  S. 
National  Museum.) 


r 


Fig.  52 

Ordovician  Brachiopods:  ^,  Lingula  rectilateralis;  2,  Orbiculoidea  tenuistriata; 
3,  4,  5,  6,  Plectambonites  sericeus;  7,  Plectambonites  centricarinatus;  8, 
Plectorthis  whitfieldi;  9,  10,  11,  Plcesiomys  retrorsa;  13,  Ploesiomys  por- 
cata;  14,  15,  Clitambonites  americanus.  (From  Ruedemann,  N.  Y.  State 
Mus.  Bui  162.} 


96 


HISTORICAL  GEOLOGY 


more  modern  aspect  than  before.  Typical  forms  are  shown  in 
Fig.  53.  Ordovician  Pelecypods,  like  their  modern  representatives 
(e.g.  Clams  and  Oysters),  appear  to  have  thrived  unusually  well 


Ordovician  Pelecypods:   a,  Cardiola  interrupta  (Hall);   b,  Orthodesmaf 
subcarinatum  (Ruedemann) ;   c,  Ambonychia  bellistriata  (Hall). 

where  muds  and  sands  were  being  deposited,  and  they  are  there- 
fore much  more  numerous  as  fossils  in  the  Upper  Ordovician  shales 
and  sandstones.  One  important  contrast  for  the  reader  to  keep  in 
mind  is  the  distribution  of  the  Pelecypod  bivalves  through  geologic 

time  as  compared  with  the  Brachi- 
opod  bivalves.  Brachiopods  were 
very  abundant  and  more  varied 
than  Pelecypods  in  the  earlier 
Paleozoic  periods,  but  they  have 
steadily  declined  almost  to  extinc- 
tion at  the  present  time,  while 
Pelecypods  have  steadily  increased 
in  numbers  and  variety  to  recent 
time. 

which  comprise  the  non-chambered,  univalve 
Mollusks,  also  deployed  to  a  marked  degree  in  this  period  and 
predominated  over  the  Pelecypods.  These  Gastropods  were  in  no 
essential  manner  different  (except  as  to  species  or  genera)  from 
existing  forms  (e.g.  the  common  Snail),  and  we  have  here  another 


Fig.  54 

Ordovician  Gastropods:  a,  Mac- 
lurea  logani  (Salter) ;  b,  Ophileta 
complanata  (Vanuxem). 


THE  ORDOVICIAN  PERIOD 


97 


of  the  few  excellent  illustrations  of  an  important  class  of  animals 
which  has  shown  surprisingly  little  change  since  early  Paleozoic 
time  (Fig.  54). 

Cevhalovods.  "The  largest,  most  powerful,  and  perhaps  the 
most  predaceous  of  the  known  forms  of  Ordovician  life  were  the 
Cephalopods,  which  seem  to  have  developed  into  prominence  with 
extraordinary  suddenness.  Unless  the  Fishes,  of  which  very  little 
is  known,  contested  their  supremacy,  they  were  doubtless  the  un- 
disputed masters  of  the  sea.  Their  relics  first  appear  at  the  time 
of  the  transition  from  the  Cambrian  to  the  Ordovician,  but  they 


o  t 


Ordovician  Cephalopods:  a,  Orthoceras  sodale  (Hall);  b,  Cyrtoceras  neleus 
(Hall);  c,  Trochoceras-like  form  (Silurian  specimen  after  Barrande);  d, 
Trocholites  ammonius  (Hall). 

were  then  so  far  advanced  and  so  widely  differentiated  from  allied 
forms  as  to  render  it  probable  that  they  had  already  lived  a  long 
time.  .  • .  .  The  size  attained  by  the  Ordovician  Cephalopods  was 
probably  never  surpassed  by  representatives  of  the  class.  Some  of 
the  shells  were  12  or  15  feet  in  length,  and  a  foot  (maximum)  in 
diameter.  From  this  great  size  they  ranged  down  to  or  below 
the  size  of  a  pipe  stem."1  These  Cephalopods  all  belonged  to 
the  Tetrabranch  or  chambered-shelled  subdivision  of  the  class 
(Fig,  55). 

1  Chamberlin  and  Salisbury:    College  Geology,  pp.  525-527. 


98 


HISTORICAL  GEOLOGY 


The  Tetrabranch  Cephalopods,  for  two  reasons,  constitute  one 
of  the  most  interesting  and  instructive  illustrations  of  evolutionary 
changes,  ranging  from  the  early  Paleozoic  to  the  present  time,  first 
because  we  have  such  an  abundant  record  in  the  rocks  of  all  these 
periods,  and  second  because  the  evolutionary  changes  have  ex- 
pressed themselves  in  the  external  or  shell  portions  in  a  remarkable 
and  easily  recognizable  manner.  The  only  known  Cambrian 
Tetrabranchs  were  of  the  very  simple,  straight,  or  curved  cham- 

bered-shelled  types  like  the  Orthoceras 
and  Cyrtoceras.  In  the  Ordovician 
the  straight  form,  e.g.  Orthoceras  (Fig. 
55 a)  was  still  dominant,  but  many  ad- 
vances were  made  giving  rise  to  more 
curved  forms  (e.g.  Cyrtoceras,  Fig. 
55b),  open-coiled  forms  (e.g.  Trocho- 
ceras,  Fig.  55c),  and  close-coiled  forms 
(e.g.  Trocholites,  Fig.  55d) .  All  of  these 
forms  belonged  to  the  Nautiloid  divi- 
sion of  the  Tetrabranchs,  that  is,  their 
septa  or  chamber  partitions,  where  in 
contact  with  the  walls  of  the  shell,  were 
straight  or  at  least  very  simple.  Close- 
coiled  Nautiloids  of  the  Ordovician 
greatly  resembled  the  modern  Pearly 
Nautilus,  which  is  one  of  the  very  few 

SKIIS8M  living  representatives  of  the  now  al- 

,H;!|B|B  most  extinct  Nautiloids  (Fig.  13) .    The 

B^SSSli  persistence  of  these  simple  close-coiled 

J™1H  '  /  forms  from  the  Ordovician  to  the  pres- 

ent is  noteworthy.  Ammonoids,  that 
is  to  say  Tetrabranchs  with  more  com- 
plex septa  junctions,  appeared  in  the 
Devonian  and  became  increasingly 
prominent  well  into  the  Mesozoic  era, 
but  they  have  not  continued  to  the 
present. 

Since  the  Tetrabranchs  are  of  such  special  interest  from  the 
standpoint  of  evolution,  the  following  tabular  summary  is  given  to 
mpre  clearly  bring  out  certain  prominent  changes  of  shell  structure 
from  Cambrian  time  to  the  present. 


Fig.  56 

An  Orthoceras  restored.  (Af- 
ter Nicholson,  from  Le 
Conte's  "Geology,"  cour- 
tesy of  D.  Appleton  and 
Company.) 


THE  ORDOVICIAN   PERIOD 


99 


Evolution  of  the  Chamber-shelled  (Tetrabranch)  Cephalopods 


QUATERNARY 


TERTIARY 


CRETACEOUS 


JURASSIC 
TRIASSIC 


PERMIAN 


MISSISSIPPIAN 
PENNSYLVANIAN 


DEVONIAN 


SILURIAN 


ORDOVICIAN 


{Chamber-shelled  Cephalopods  rep- 
resented only  by  a  few  genera  of 
close-coiled  Nautiloids,  e.g.  mod- 
ern Pearly  Nautilus  (Fig.  13). 

(  Ammonoids  very  rare  and  in  lowest  1 

\      Tertiary  (Eocene)  only.  Close    coiled    Nauti- 

Ammonoids     much     like    Jurassic  I       loids  only  persist, 

though  somewhat  diminished  and  f      e.g.  Nautilus,   but 

with  straight  forms  (e.g.  Baculi- 

tes,   Fig.f  16 If),  and   curved   or 

open-coiled  forms  more  common. 

Ammonoids  greatly  advanced  in 
numbers,  species,  and  complexity 
of  septa,  and  they  reach  their 
climax,  e.g.  Ceratite  with  scal- 
loped septa  (Fig.  127) ;  Ammonite 
with  highly  frilled  septa  (Fig.  141) ; 
and  some  curved  and  straight 
Ammonoids. 


more  varied   than 
now. 


Some  Nautiloids  pre- 
sent, but  Orthoce- 
ras  becomes  extinct 
in  Triassic. 


Ammonoids  common,  some  showing 
distinctly  increased  (highly 
curved)  complexity  of  septa  (e.g. 
Waagenoceras,  Fig.  115). 

Much  like  Devonian,  but  complex- 
ity of  septa  in  Goniatites  some- 
what increased. 

Ammonoids  first  appear  with  only 
slight  (angular)  complexity  of 
septa  junctions,  e.g.  Goniatite 

(Fig.  77). 

Much  like  Ordovician.  No  Ammo- 
noids. 

Close-coiled  forms,  e.g.  Trocholites 

(Fig.  55d). 
Open-coiled    forms,    e.g.    Trochoc- 

eras  (Fig.  55c). 
Curved     forms,     e.g.      Cyrtoceras 

(Fig.55b). 
Straight     forms,     e.g.     Orthoceras 

(Fig.  55a). 


Nautiloids,  including 
Orthoceras,  persist, 
but  subordinate. 


Nautiloids   still 
dominate. 


pre- 


Simpler  forms  (Nau- 
tiloids) continue  as 
in  Silurian. 

Coiled  Nautiloid- 
forms  predominate. 


Straight  forms  pre- 
dominate. 


CAMBRIAN 


Straight  and  curved  forms  only. 


100 


HISTORICAL  GEOLOGY 


Arthropods.  —  Crustaceans  were  represented  by  both  Trilobites 
and  Eucrustaceans.  Trilobites,  which  were  the  chief  Ordovician 
Arthropods,  reached  their  climax  or  culmination  of  development 
in  numbers  and  species,  more  than  a  thousand  species  being 
known  from  the  Ordovician  alone  (Fig.  58).  These  animals,  after 
the  Brachiopods,  appear  to  have  been  among  the  most  numerous 
animals  of  the  time.  Their  variation  in  size  was  much  like  that  of 
the  Cambrian,  but  their  eyes  were  usually  larger  and  better 
developed.  Eucrustaceans  were  represented  by  comparatively 
few  simple  forms,  e.g.  Ostracods  and  Cirripeds  (Barnacles). 


f 


a  b 

Fig.  57 

Bits  of  Ordovician  sea-bottom:  a,  Brachiopod  shells  on  limestone;  6,  Crinoid, 
Bryozoan,  Brachiopod,  Pelecypod,  Gastropod,  and  Cephalopod  remains  in 
calcareous  sandstone.  (W.  J.  Miller,  photos.) 

Arachnids,  which  date  from  Algonkian  time,  were  represented, 
though  not  abundantly,  by  the  remarkable  group  of  Eurypterids. 
Since  these  creatures  reached  a  much  fuller  development  during  the 
Silurian  period,  further  discussion  is  reserved  for  the  next  chapter. 

Insects  are  not  known  to  have  existed  during  this  period. 


THE  ORDOVICIAN;  PERIOD 


Fig.  58 

Ordovician  Trilobites:  1,  la,  Triarthrus  becki  (restorations  by  Beecher); 
2,  2a,  Bumastus  trentonensis;  2,  Acidaspis  crosotus;  4,  Trinucleus  concen- 
tricus;  5,  Bronteus  lunatus;  6,  Ceraurus  pleurexanthmus;  7,  Isotelus  maxi- 
mus;  8,  8a,  Calymmene  calicephala.  (From  Scott's  "  Introduction  to  Ge- 
ology," permission  of  The  Macmillan  Company.) 


102  HISTORICAL  GEOLOGY 

Vertebrates.  —  From  the  standpoint  of  evolution,  perhaps  the 
most  significant  feature  of  the  Ordovician  is  the  occurrence  of  the 
earliest  known  vertebrates.  These  were  very  primitive  fishlike 
forms  such  as  Ostracoderms,  which  have  been  found  in  Ordovician 
strata  at  certain  places  in  Colorado  and  Wyoming.  The  fossils 
are  mostly  very  fragmentary,  consisting  chiefly  of  scaJ£a^or_plates, 
but  some  nearly  complete  dermal  plates  are  known.  They  strongly 
suggest  the  Ostracoderms,  but  since  such  forms  are  much  better 
known  from  the  Devonian,  we  shall  postpone  a  fuller  discussion 
of  these  curious  creatures. 


CHAPTER  VIII 


THE    SILURIAN    (UPPER    SILURIAN)    PERIOD 
ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

WE  have  already  learned  how  the  great  body  of  lowest  fossil- 
iferous  strata  in  the  British  Isles  was  called  the  Silurian  system  by 
Murchison  in  1835.  The  name  was  derived  from  Silures,  an  old 
tribe  which  once  lived  in  part  of  Wales.  In  the  preceding  chapter 
we  have  also  shown  how  the  Silurian  has  since  been  divided  into 
three  systems  —  Cambrian,  Ordovician,  and  Silurian.  In  view  of 
the.  priority  of  Murchison's  term  "  Silurian,"  and  the  fact  that  the 
Ordovician  strata  are  now  known  to  be  more  important  and  wide- 
spread than  those  we  call  Silurian,  it  seems  inappropriate  that 
the  terms  Ordovician  and  Silurian  are  not  employed  in  the  reverse 
order. 

Since  the  Silurian  strata,  too,  were  first  carefully  studied  in 
New  York,  the  section  for  that  state  becomes  to  a  very  considerable 
degree  a  standard  of  comparison  for  all  American  Silurian  strata. 
Like  the  Cambrian  and  Ordovician  systems,  the  Silurian  is  gener- 
ally subdivided  into  three  major  portions  or  series,  these  in  turn 
being  subdivided  into  various  stages.  The  most  recent  classi- 
fication by  the  New  York  Geological  Survey  is  as  follows: 

Manlius  limestone. 

Rondout  waterlime. 

Cobleskill  limestone. 

Salina  shale,  salt,  and  waterlime  (also  the 

Shawangunk  conglomerate) . 
Guelph  dolomite 
Lockport  dolomite 


SILURIAN 

SYSTEM 


Cayugan  series 
(Upper  Silurian) 


Niagaran  series 


Niagara  limestone. 


(Middle  Silurian)  1  Clinton  shale,  limestone,  sandstone,  and  iron 
I      ore. 
f  Medina  and  Oneida  sandstone,  conglomer- 

OM     .     N    ]      ate,  and  shale. 
(Lower  Silurian)    (  Ogwego  gandstone 


Oswegan  series 


The  New  York  Silurian  section  is  more  complete  than  the 
Ordovician,  because  the  unconformities  are  fewer  and  of  lesser 

103 


104  HISTORICAL  GEOLOGY 

importance,  so  that  few  horizons  are  missing.  As  was  stated  in 
connection  with  the  Ordovician,  so  here,  it  should  be  remembered 
that  many  formation  or  stage  names  have  been  more  or  less  locally 
applied  in  North  America  to  formations  not  yet  definitely  cor- 
related with  those  of  New  York,  or  to  a  few  others  not  represented 
in  New  York.  Also  the  lithologic  character  of  formations  may  be 
quite  different  in  different  regions. 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution. — The  present  surface  distribution  of  the 
Silurian  rocks  in  North  America  is  shown  on  map,  Fig.  59,  which 
is  largely  self-explanatory.  Certain  points  of  comparison  with  the 
Ordovician  (see  map,  Fig.  41)  need  to  be  mentioned.  Thus  to  a 
very  considerable  degree  the  Silurian  and  Ordovician  rocks  occur 
in  the  same  areas,  the  chief  differences  being  much  more  extensive 
areas  of  Silurian  strata  in  the  Arctic  Islands  region,  their  almost 
complete  absence  from  the  upper  St.  Lawrence  Valley,  and  their 
much  smaller  representation  in  the  mid-Mississippi  Basin,  Rocky 
Mountains,  and  Great  Basin  of  the  west. 

As  stated  in  connection  with  the  two  preceding  areal  distribu- 
tion maps,  so  here,  the  surface  distribution  of  Silurian  rocks  by  no 
means  indicates  the  former  or  even  present  actual  extent  of  these 
rocks  in  North  America.  From  many  regions  Silurian  strata  have 
been  removed  by  erosion,  while  in  other  regions  they  are  concealed 
under  cover  of  later  rocks.  Thus  most  of  the  upper  Mississippi 
Basin,  with  its  essentially  horizontal  strata,  is  underlain  with 
Silurian  rocks,  and  only  the  eroded  edges  of  upturned  Silurian 
strata  are  exposed  in  the  Appalachian  Mountains. 

The  Oswegan  Series.  —  This  series,  in  the  northeastern  United 
States,  consists  principally  of  the  Oswego  sandstone,  and  Medina 
sandstone,  shale,  and  (Oneida)  conglomerate.  Ripple-marks, 
cross-bedding,  and  the  character  of  the  fossils  prove  these  to  have 
been  deposited  in  a  very  shallow,  probably  encroaching,  sea.  The 
Oneida  conglomerate  is  made  up  of  well-rounded  pebbles,  bears 
all  the  marks  of  a  typical  marine-beach  or  very  shallow-water 
deposit,  and  in  central  New  York  rests  upon  the  eroded  edges  of 
the  Upper  Ordovician  shales. 

The  Niagaran  Series.  —  This  series  is  of  special  interest  both 
because  of  its  lower  or  Clinton  beds  and  its  higher  or  Lockport  and 


THE  SILURIAN  PERIOD 


105 


Guelph  dolomitic  limestones.     The  Clinton  formation  rests  con- 
formably upon  the  Medina  beds,  but  is  more  widespread  than  they. 


Fig.  59 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Silurian  strata  in 
North  America.  (Modified  by  W.  J.  M.  after  Willis,  U.  S.  Geological 
Survey.) 

It  extends  through  the  Appalachian  Mountains,  westward  from 
central  New  York  to  Lake  Huron  and  Indiana  into  Wisconsin, 
and  probably  through  Illinois  and  Missouri.  It  is  also  known  in 


106  HISTORICAL  GEOLOGY 

Nova  Scotia.  Lithologically  this  formation  is  quite  variable, 
being  mostly  shales  and  sandstones  in  the  Appalachians  and 
central  New  York,  and  largely  limestone  in  western  New  York  and 
farther  west  and  southwest.  This  limestone  does  not  imply  deep 
marine  water,  but  merely  shallow  water  comparatively  free  from 
land-derived  sediments.  A  remarkable  and  well-nigh  universal 
feature  of  the  Clinton  formation  is  its  interstratified  beds  of  iron 
ore  (hematite) .  This  iron  ore  is  especially  well  developed  through- 
out the  Appalachians,  from  central  to  western  New  York, 
Wisconsin,  and  in  Nova  Scotia.  The  ore  is  concretionary  or  oolitic 
in  character  and  apparently  a  contemporaneous  deposit  enclosed 
within  the  shales  or  limestones.  It  is  often  highly  fossiliferous, 
hence  the  name  " fossil  ore." 

i  Conformably  above  the  Clinton  beds  lies  the  Niagara  limestone, 
which  has  a  still  wider  distribution  than  the  Clinton.  Its  type 
locality  is  at  Niagara  Falls,  and  in  New  York  state  it  is  divided 
into  the  Lockport  and  Guelph  dolomitic  limestone  formations. 
This  mid-Silurian  time  was  another  great  limestone-making  age 
almost  comparable  to  that  of  the  mid-Ordovician.  In  the  United 
States,  Niagara  limestone  is  known  throughout  much  of  the  upper 
Mississippi  Valley  and  Great  Lakes  region,  southward  to  Ten- 
nessee, and  westward  to  Missouri,  Oklahoma,  and  northern  Texas. 
In  Canada  it  is  widely  distributed  in  Manitoba,  just  west  of 
Hudson  Bay,  and  in  the  Arctic  Islands.  Niagara  limestone  also 
quite  certainly  occurs  in  parts  of  the  western  United  States, 
though  definite  correlations  are  not  yet  made.  Coral  reefs  are  of 
common  occurrence  in  the  formation.  It  should  not  be  understood, 
however,  that  limestone  was  universally  forming  during  Niagara 
time,  exceptions  being,  for  example,  Niagara  shales  in  central 
New  York  and  in  Nova  Scotia. 

The  Cayugan  Series.  —  The  Salina  formation  rests  directly 
upon,  but  is  much  less  extensive  than,  the  Niagara  formation, 
being  found  only  through  parts  of  Pennsylvania,  New  York, 
Ontario,  Ohio,  and  Michigan.  Lithologically  the  formation  is 
quite  variable,  including  all  the  common  types  of  sediments  as 
well  as  waterlime  (hydraulic  limestone),  red  shales,  and  salt  and 
gypsum  beds.  The  Shawangunk  conglomerate,  until  quite  recently 
classed  with  the  Oneida,  is  of  Salina  age.  The  eroded  edges  of  its 
resistant,  tilted  strata  form  the  Shawangunk  Ridge  (so-called 
Range)  of  southeastern  New  York  and  the  Kittatinny  Range  (5f 


THE  SILURIAN  PERIOD  107 

New  Jersey  and  Pennsylvania.  The  Delaware  Water  Gap  is  cut 
through  this  formation. 

Overlying  the  Salina  beds,  but  considerably  more  extensive, 
are  the  limestones  and  waterlimes  of  Cobleskill,  Rondout,  and 
Manlius  ages  which  reach  from  Pennsylvania  and  New  York  west- 
ward to  Indiana  and  Wisconsin. 

Silurian  of  the  West.  —  Definite  subdivisions  and  correlations 
of  the  Silurian  strata  of  the  West  have  not  yet  been  made,  but  in 
certain  regions,  like  the  Great  Basin,  there  appears  to  be  a  prac- 
tically unbroken  succession  of  largely  limestone  strata  ranging  in 
age  from  Middle  Ordovician  (Trenton)  to  Devonian. 

Thickness  of  the  Silurian.  —  From  central  to  western  New 
York  the  thickness  of  the  Silurian  system  is  from  1000  to  1500 
feet.  Its  maximum  thickness  is  from  2000  to  4000  feet  in  the 
Appalachians,  while  in  the  Mississippi  Valley  the  thickness  is 
generally  less  than  1000  feet.  The  Niagara  limestone  is  a  notable 
exception  to  the  usually  greater  thickness  of  the  early  Paleozoic 
strata  in  the  Appalachian  region,  since  in  Wisconsin  it  is  some  700 
or  800  feet  thick,  while  in  the  east  it  is  only  from  100  to  300  feet. 

Igneous  Rocks.  —  In  North  America  the  only  igneous  rocks 
regarded  as  of  Silurian  age  are  some  in  Maine,  Nova  Scotia,  and 
New  Brunswick.  Igneous  intrusives  of  later  date  have  sometimes 
penetrated  Silurian  strata. 


PHYSICAL  HISTOEY 

Early  and  Middle  Silurian.  —  We  have  learned  that,  as  a 
result  of  physical  disturbance  toward  the  close  of  the  Ordovician, 
much  of  the  interior  Paleozoic  sea  was  drained,  causing  the  land 
area  to  be  so  much  enlarged  as  to  have  been  more  extensive  than 
at  any  time  since  the  beginning  of  the  Paleozoic  era.  This  was 
essentially  the  geographic  condition  of  the  continent  at  the  begin- 
ning of  the  Silurian.  The  boldest  topographic  feature  was  the 
presence  of  the  newly  formed  Taconic  Range  along  the  Atlantic 
sea-board.  Doubtless  there  were  some  areas  of  sedimentation, 
but  our  present  knowledge  of  the  earliest  Silurian  physiography 
of  North  America  does  not  admit  of  their  delimitation. 

This  condition  of  the  continent  was  not  of  (geologically)  long 
duration,  because  pretty  early  in  the  Silurian  another  great  trans- 
gression of  the  sea  took  place,  gradually  increasing  the  extent  of 


108  THE  SILURIAN  PERIOD 

the  marine  waters  to  a  maximum  in  the  mid-Silurian  (Niagaran) 
epoch.  On  the  accompanying  map  (Fig.  60),  the  relations  of  land 
and  water  are  graphically  depicted,  and  it  will  be  seen  that  the 
extent  of  marine  waters  was  almost  comparable  to  that  of  mid- 
Ordovician  time,  though  with  the  following  chief  differences  in  the 
mid-Silurian:  Appalachia  was  larger  and  higher  because  of  the 
Taconic  uplift;  the  land  areas  east  and  west  of  Hudson  Bay  and  in 
the  Cordilleran  region  were  larger;  and  there  was  more  land  in 
the  Gulf  border  (especially  Texas)  region.  That  this  Niagaran  sea 
was  a  true  epicontinental  or  shallow  water  body  is  definitely  known 
for  reasons  similar  to  those  given  in  the  discussion  of  the  mid- 
Ordovician  sea. 

In  order  to  further  impress  upon  the  reader  not  only  how  a 
marine  transgression  of  this  sort  is  proved,  but  also  how  the  direc- 
tion of  encroachment  can  be  determined,  we  may  briefly  consider 
the  excellent  example  afforded  by  the  disposition  of  Silurian  strata 
in  New  York  state.  That  central  and  western  New  York  were 
submerged  before  the  Hudson  Valley  region  is  proved  as  follows. 
In  central  New  York  the  first  deposit  to  form  upon  the  eroded  sur- 
face of  the  Ordovician  shales  was  the  Oneida  conglomerate.  In 
the  Hudson  Valley  of  New  York  (e.g.  Shawangunk  Range),  the 
first  deposit  to  be  laid  down  upon  the  eroded  Ordovician  shales 
was  the  Shawangunk  conglomerate  which  belongs  with  the  Salina 
division  and  is  therefore  much  younger  than  the  Oneida  conglom- 
erate. Also  the  Clinton  and  Niagara  formations,  well  developed 
in  central  and  western  New  York,  were  never  formed  in  the  east- 
ern or  southeastern  parts  of  the  state,  though  they  do  extend 
somewhat  farther  eastward  than  the  Oneida.  Thus  we  prove 
that  the  Silurian  sea  overspread  central  and  western  New  York 
long  before  it  reached  the  Hudson  Valley  region  of  southeastern 
New  York. 

Late  gilurian.  —  Two  prominent  events  mark  the  physical 
history  of  late  Silurian  time,  namely  a  very  considerable  with- 
drawal of  the  extensive  (Niagaran)  sea  in  early  Cayugan  (Salina) 
time,  and  a  considerable,  though  only  partial,  reextension  of  the 
sea  in  later  Cayugan  time.  That  a  very  appreciable  retrogression 
of  the  Niagaran  sea  ushered  in  Salina  time  is  proved  by  both  the 
comparatively  restricted  distribution  and  the  character  of  the 
Salina  strata.  Thus  in  the  eastern  United  States  and  Canada 
Salina  strata  occur  only  through  parts  of  Pennsylvania  and  south- 


SILURIAN 

>RTH     AMERICA 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAND 
LANDS 
INDETERMINATE  AREAS 

POLAR 
EQUATO 


^        I  TEMPORARY  LAND 


Fig.  60 

Paleogeographic  map  of  North  America  in  the  Silurian  period.    (Slightly  modi- 
fied after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.) 


110  HISTORICAL  GEOLOGY 

ward  to  Virginia  in  the  Appalachians,  New  York,  Ontario,  Ohio, 
and  Michigan,  and  are  quite  generally  characterized  by  red  shales 
and  sandstones  and  salt  and  gypsum  deposits.  Such  materials 
imply  arid  climate  conditions,  with  deposition  in  extensive  lagoons 
or  more  or  less  cut-off  arms  of  the  sea,  rather  than  typical  open 
sea  conditions. 

Since  the  immediately  overlying  Cayugan  formations  (Coble- 
skill,  Rondout,  and  Manlius)  are  mostly  marine  deposits  and  more 
extensive  than  the  Salina,  it  is  evident  that  there  was  at  least  a 
partial  restoration  of  more  widespread  marine  waters  during  later 
Cayugan  time.  This  later  Cayugan  sea  spread  from  eastern  New 
York  westward  over  the  Salina  lagoon  areas  and  into  eastern 
Wisconsin,  and  from  eastern  New  York  southward  through  the 
Appalachian  district.  So  far  as  known  the  rest  of  the  continent 
was  dry  land. 

In  addition  to  these  broader  and  more  important  geographic 
changes  during  the  Silurian  period,  there  were  of  course  various 
minor  and  generally  local  changes  of  relative  level  between  land 
and  sea,  some  of  these  now  being  known  and  some  not  yet  deter- 
mined. 

Close  of  the  Silurian.  —  At  the  close  of  the  Silurian,  or  opening 
of  the  Devonian,  the  Cayugan  sea  withdrew  from  the  area  from 
central  New  York  to  Wisconsin,  and  but  a  few  comparatively 
small  areas  of  eastern  North  America  were  submerged,  as  shown  on 
map  (Fig.  69) .  This  was  essentially  the  geography  of  the  conti- 
nent in  earliest  Devonian  time  and  will  be  discussed  in  the  next 
chapter. 

There  appear  to  have  been  no  mountain-making  (orogenic) 
movements,  and  no  important  epeirogenic  disturbances  at  the  close 
of  the  Silurian  in  North  America.  Because  of  the  comparatively 
quiet  and  gradual  transition  into  the  succeeding  period,  the  Silurian 
and  Devonian  systems  are  usually  not  sharply  separated  from  each 
other,  and  often,  as  in  New  York,  there  has  been  difficulty  in 
satisfactorily  dividing  the  systems. 

FOREIGN  SILURIAN 

The  Ordovician  division  of  Europe  into  two  great  provinces  or 
basins  of  deposition  —  northern  and  southern  —  was  continued  in 
the  Silurian,  though  the  latter  strata  are  not  so  widely  distributed. 


THE  SILURIAN  PERIOD 


111 


The  faunas  of  these  two  provinces  show  greater  differences  than 
does  the  northern  province  as  compared  with  North  America,  or 
even  other  continents.  This  implies  a  lack  of  free  communication 
between  the  southern  European'  province  and  the  more  typical 
Silurian  provinces  of  the  earth. 

As  in  America,  European  Silurian  strata  are  largely  concealed 
beneath  later  formations.    Usually  the  Silurian  rests  conformably 


Fig.  61 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe 
during  Silurian  time.  Dotted  areas,  water.  (Slightly  modified 
after  De  Lapparent.) 

upon  the  Ordovician,  except  in  the  British  Isles.  Also  in  most  of 
Europe  the  transition  to  the  Devonian  was  gradual,  except  in  the 
British  Isles,  where  the  Silurian  strata  were  tilted  and  eroded  before 
the  deposition  of  the  Devonian.  In  much  of  the  southern  province 
the  rocks  are  folded  and  tilted,  though  this  deformation  took  place 
sometime  after  the  close  of  the  Silurian.  In  mid-Silurian,  as  in 
North  America,  much  limestone  was  formed  across  the  British 
Isles,  southern  Scandinavia,  and  well  into  Russia.  Silurian  strata 


112  HISTORICAL  GEOLOGY 

of  Europe  are  not  as  thick  as  those  of  the  two  immediately  preced- 
ing systems,  being  from  3000  to  5000  feet  in  the  British  Isles,  and 
generally  less  elsewhere.  Igneous  rocks  of  Silurian  age  are  almost 
unknown. 

In  other  continents  Silurian  rocks  have  seldom  been  well  studied 
and  separated  from  the  Ordovician,  though  they  are  definitely 
known  in  China,  Africa,  Australia,  and  South  America. 

CLIMATE 

The  general  distribution  and  character  of  the  rocks  and  their 
fossil  content  point  to  more  uniform  climatic  conditions  than  those 
of  today.  Fossils  in  the  Arctic  Silurian  rocks  are  not  essentially 
different  from  those  of  low  latitudes. 

From  central  New  York  across  to  Michigan  at  least,  there  was 
an  arid  climate  during  the  Salina  epoch,  as  already  mentioned,  but 
this  was  probably  only  local. 

ECONOMIC  PRODUCTS. 

Silurian  sandstones  and  limestones  are  extensively  quarried  for 
building  purposes,  or  the  limestones  burned  to  make  quick-lime. 
The  waterlimes  of  late  Silurian  age  were  until  quite  recently  con- 
siderably used  for  the  manufacture  of  hydraulic  cement,  especially 
in  the  Hudson  Valley  of  New  York  state. 

We  mentioned  the  widespread  and  almost  universal  occurrence 
of  hematite  iron  ore  in  the  Clinton  formation.  This  ore  is  mined  to 
some  extent  in  central  and  western  New  York,  but  in  the  Birming- 
ham, Alabama,  district,  which  is  the  second  greatest  iron  mining 
region  of  America,  the  Clinton  formation  is  the  source  of  the  ore. 

Another  important  economic  product  of  Silurian  age  is  the  salt 
of  the  Salina  formation.  In  New  York  alone  salt  beds  underlie 
most  of  the  western  part  of  the  state  or  an  area  of  about  10,000 
square  miles.  Sometimes  there  is  one  bed  and  sometimes  several 
interstratified  with  other  rocks.  Single  beds  locally  attain  a  thick- 
ness of  from  50  to  80  feet.  In  the  southern  part  of  the  state  the 
salt  is  most  deeply  buried  under  later  rocks,  a  well  at  Ithaca  having 
passed  through  248  feet  of  salt  in  seven  beds  below  2244  feet  from 
the  surface.  Toward  the  north  the  beds  gradually  come  near  the 
surface.  Important  salt  beds  also  occur  near  Cleveland,  Ohio, 


THE  SILURIAN  PERIOD  113 

and  Saginaw,  Michigan.  The  usual  method  of  obtaining  the  salt 
is  by  pumping  brine  from  deep  wells,  and  then  evaporating. 

Much  gypsum  is  mined  along  the  lines  of  outcrop  of  Cayugan 
strata  in  western  New  York. 

Oil  and  gas  are  obtained  from  the  Clinton  sandstone  of  Ohio, 
and  some  gas  from  the  Medina  sandstone  of  New  York. 

LIFE  OF  THE  SILURIAN 

Plants.  —  Sea-weeds,  though  not  abundant  as  fossils,  are  well 
known,  especially  in  the  Medina-Oneida  sandstones  and  con- 
glomerate, and  Clinton  formation,  all  of  which  were  deposited  in 
very  shallow  water.  Knowledge  of  the  land  plants  of  the  period 
is  still  very  meagre,  though  some  rather  doubtful  specimens  are 
known.  Perhaps  the  most  authoritative  example  is  a  fossil  Fern 


a  b 

Fig.  62 

Silurian  and  Devonian  Corals:  a,  Cup-coral,  Zaphrentis  roemeri  (M.  Edwards 
and  Haime)  (Devonian  form);  b,  Honeycomb-coral,  Heliolites  pyriformis 
(Guettard);  Chain-coral*,  Holy  sites  catenulatus  (Linn.). 

found  in  France,  and  this  shows  that  the  Pteridophytes  at  least 
were  in  existence.  Considering  the  profuse  land  vegetation  of  the 
next  (Devonian)  period,  it  seems  certain  that  their  progenitors 
must  have  been  well  represented  in  the  Silurian,  and  that  either 
their  remains  may  yet  be  discovered,  or  the  conditions  for  their 
preservation  were  unfavorable. 

Protozoans  have  not  been  found  as  fossils,  but  they  must  have 
existed,  because  they  are  known  from  both  the  preceding  and  suc- 
ceeding periods. 

Porifers.  —  Sponges  were  common,  and  in  the  Silurian  strata 
of  western  Tennessee  they  are  exceedingly  abundant.  A  genus  of 


114 


HISTORICAL  GEOLOGY 


nearly  spherical  forms  with  deep  grooves  was  particularly  promi- 
nent. 

Coelenterates.  —  Graptolites,    though    greatly    diminished    in 
importance,  were  still  fairly  common.    The  more  complex  colonies, 

such  as  branching  forms 
and  those  with  double 
rows  of  cells  on  their 
axes,  were  nearly  ex- 
tinct, the  simple  forms 
mostly  only  remaining. 
Anthozoans  (Corals) 
increased  in  prominence 
to  a  very  notable  de- 
gree, and  the  simple 
Cup  Corals  (Fig.  62a) 
of  the  Ordovician  were 
superseded  in  impor- 
tance by  the  coloniz- 
ing or  compound  forms. 
Chain  Corals  (Fig.  62c), 
which  were  rare  in 
the  Ordovician,  reached 
their  climax  of  de- 
velopment, but  became 
nearly  extinct  by  the 
close  of  the  period. 
Honeycomb  Corals  (Fig. 
62 b)  were  also  common. 
Echinoderms.— 
Though  the  Cystoids 
reached  their  climax  in 
the  Ordovician,  they 
were  still  abundant  in 
the  Silurian,  the  Ni- 
agara limestone  near 
Chicago  being  particularly  rich  in  them.  Many  were  unusually 
large,  and  some  showed  greater  degree  of  symmetry  in  arrange- 
ment of  plates  than  before  (Fig.  63a). 

Blastoids  still  remained   rare,  only  two  genera  being  known 
(Fig.  63b). 


Fig.  63 

Silurian  Echinoderms:  a,  Cystoid,  Caryocrinus 
qrnatus;  b,  Blastoid,  Troostocrinus  reinwardti; 
c,  Crinoid,  Eucalyptocrinus  crassus.  (After 
Say,  Troost,  and  Hall  respectively.) 


THE  SILURIAN  PERIOD 


115 


Crinoids  very  considerably  increased  in  numbers  and  species 
as  well  as  in  complexity  of  structure  (Fig.  63 c).  "They  attained 
such  abundance  in  certain  localities  that  their  fragments  formed 
the  main  substance  of  the  limestone.  These  spots  became  veritable 
'flower-beds'  of  'stone  lilies/  and  certain  localities,  as  Lockport, 
N.  Y.,  Waldron  and  St.  Paul,  Ind.,  Racine,  Wis.,  Chicago,  111., 
Gotland,  Sweden,  and  Dudley,  England,  have  become  noted  as 
peculiarly  rich  crinoidal  fields,  where  beautiful  and  varied  forms 


Fig.  64 

Silurian    Trilobites:     a,    Sphcerexochus   mirus    (Bey.) ;     b,    Staurocephalus 
murchisoni  (Barr.);    c,  Deiphon  forbesi  (Barr.);    d,  Calymene  niagarensis 
'(Hall);   e,  Cyphaspis  christyi  (Hall).    (From  Chamberlin  and  Salisbury's 
"Geology,"  courtesy  of  Henry  Holt  and  Company.) 

grew  in  groves,  as  it  were."1  About  400  species  are  known  from 
the  Silurian  of  North  America. 

Aster 'ozoans  (Star-fishes)  and  Echinoids  (Sea-urchins)  became 
more  common,  though  by  no  means  abundant.  Modern  Sea-urchins 
have  exactly  twenty  rows  of  calcareous  plates  tightly  fitted  to- 
gether, while  Paleozoic  forms  had  a  variable  number  of  plates,  and 
in  some  forms  the  plates  were  only  loosely  joined  together,  this 
latter  feature  apparently  being  a  primitive  characteristic. 

Molluscoids.  —  Bryozoans  were  less  prominent  than  in  the 
Ordovician,  but,  nevertheless,  they  were  often  common  as  reef 
1  Chamberlin  and  Salisbury:  Geology,  Vol.  2,  p.  400. 


116 


HISTORICAL  GEOLOGY 


builders.     Their  lack  of  abundance  may  be  somewhat  apparent 
only,  due  to  the  fact  that  more  delicate  forms  prevailed.. 


Fig.  65 

A  Silurian  Eurypterid,  Eurypteris  remipes,  restored  to  show 
dorsal  side.  (After  Clarke  and  Ruedemann,  N.  Y.  State 
Mus.  Mem.  14.) 

Brachiopods  continued  to  be  the  most  prominent  of  all  organ- 
isms as  regards  both  number  of  individuals  and  species,  and  this  in 
spite  of  the  fact  that  very  few  Ordovician  species,  and  not  many 
genera,  continued  from  the  Ordovician  into  the  Silurian.  Two 


THE  SILURIAN  PERIOD 


117 


genera,  Spirifer  and  Pentamerus,  made  their  first  appearance  and 
were  especially  prominent  in  the  Silurian,  but  became  even  more 
so  in  the  Devonian.  The  Spirifer  developed  a  long,  straight,  hinge 
line,  while  the  Pentamerus  had  a  sort  of  hook-shaped  beak  pro- 
jecting over  the  hinge  line. 

Mollusks.  —  The  Pelecy- 
pods  and  Gastropods  were  still 
common,  but  they  were  in  no 
important  way  different  from 
those  of  the  preceding  period. 

Cephalopods  were  repre- 
sented only  by  the  Nautiloids. 
Of  these,  the  straight  (Ort hoc- 
eras)  forms  were  still  com- 
mon, but  the  curved  and 
coiled  forms  became  predom- 
inant. Some  of  the  Nautiloids 
were  notably  ornamented  ex- 
ternally. Otherwise,  except 
for  many  genera  and  species 
changes,  the  Cephalopods 
were  much  like  those  of  the 
Ordovician,  which  we  rather 
fully  discussed. 

Arthropods.  —  Crustaceans 
were  represented  by  Mero- 
stomes,  Trilobites  and  Eucru- 
staceans.  Horse-shoe  Crabs, 


Fig.  66 

A  Silurian  Scorpion,  Paleophonus  cale- 
donicus,  by  Hunter  after  Peach. 
(From  Le  Conte's  "  Geology,"  per- 
mission of  D.  Appleton  and  Com- 
pany.) 


representing  the  Merostomes, 
first  appeared  in  the  Silurian. 
Trilobites  culminated  in  the 
preceding  period,  but  they 
still  continued  to  be  common. 
A  few  new  genera  appeared,  but  more  disappeared.  Silurian  Tri- 
lobites were  perhaps  more  diversified  than  in  any  other  period. 
"  Like  the  decadent  nations  revealed  to  us  in  human  history, 
they  indulged  in  extravagant  and  futile  eccentricities,  ill  befitting 
their  approaching  overthrow.  Odd  and  highly  ornate  forms 
appeared  in  profusion  (Fig.  64b,  c),  and  in  most  instances  the 
spines,  tubercles,  and  horns  which  they  produced  seem  to  have 


118 


HISTORICAL  GEOLOGY 


had  little  or  no  real  value  in  their  life  activities.  We  shall  see  in 
studying  later  periods  that  similar  eccentricities  mark  the  fall  of 
other  groups,  such  as  the  Ammonites  and  the  Reptiles. " 1  Eucrus- 
taceans  were  much  like  those  of  the  Ordovician. 

Arachnids,  represented  by  the  Eurypterids,  greatly  increased 
in  numbers,  species,  and  size,  and  they  appear  to  have  culmi- 
nated in  this  period.  The 
following  brief  description, 
together  with  an  examina- 
tion of  Fig.  65,  will  serve 
to  give  a  fair  idea  of  the 
appearance  and  structure 
of  these  remarkable  crea- 
tures. In  the  typical 
Eurypterid,  a  quadrate  or 
semicircular  head  has  be- 
hind it  twelve  movable 
segments  making  up  the 
abdomen,  and  attached  to 
the  last  segment  is  either 
a  spine  or  plate-like  tail. 
The  five  pairs  of  append- 
ages all  come  out  from  the 
head  portion,  thus  being 
markedly  different  from 
the  Trilobites.  The  first 
pair  of  appendages  are 
much  enlarged,  sometimes 
provided  with  pincers  and 
sometimes  not,  while  the 
fifth  pair  are  usually  long 
and  they  serve  as  swim- 
ming paddles.  They  varied  greatly  in  size,  one  species,  from  the 
Silurian,  having  attained  a  length  of  over  six  feet  and  so  is  one  of 
the  largest  known  Arthropods.  Many  Eurypterids  appear  to  have 
been  marine  animals,  while  others  probably  lived  in  fresh  or  brack- 
ish water  lagoons.  The  Arachnids  included  also  the  earliest  known 
Scorpions  (Fig.  66),  which  were  in  many  respects  similar  to  the 
Eurypterids. 

1  Blackwelder  and  Barrows:  Elements  of  Geology,  pp.  352-353. 


A    bit    of 
Crinoid, 


Fig.  67 

Silurian    sea-bottom    showing 
Bryozoan,     Brachiopod,     and 


Trilobite  remains.    (W.  J.  Miller,  photo.) 


THE  SILURIAN  PERIOD  119 

Insects  are  not  known  from  the  Silurian. 

Vertebrates.  —  The  only  known  Silurian  Vertebrates  were  of 
very  simple  types,  such  as  the  Ostracoderms  and  primiflV  ffVsfe/^ 
probably  Sharks.  All  of  the  Ostracoderms  were  small,  odd-shaped 
creatures,  but  pretty  closely  related  to  the  more  prolific  Devonian 
forms  to  be  described  later. 


CHAPTER  IX 

THE    DEVONIAN    PERIOD 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

IN  1839  Sedgwick  and  Murchison  gave  the  name  of  Devonian  to 
strata  in  the  county  of  Devonshire  in  England  where  rocks  of  this 
age  were  first  carefully  studied.  Because  of  the  metamorphosed 
and  highly  disturbed  character  of  the  English  Devonian,  the 
sub-divisions  in  Europe  were  not  well  worked  out  until  the  more 
undisturbed  rocks  of  Belgium  and  along  the  Rhine  were  studied. 

In  North  America  the  New  York  subdivisions  are  taken  as  the 
standard,  because  the  Devonian  strata  were  first  carefully  studied 
there.  The  New  York  Devonian  section  is  a  remarkably  complete 
one  of  very  considerable  thickness  (fully  4000  feet),  with  not  a 
single  stage  missing,  except  possibly  the  very  lowest  one,  and  with 
a  surface  distribution  over  fully  one-third  of  the  area  of  the  state. 
There  was  well  nigh  continuous  deposition  of  strata  during  Devo- 
nian time  in  New  York,  and  if  locally  a  stage  or  sub-stage  is  missing, 
it  is  present  elsewhere  in  the  state.  It  is  doubtful  if  a  greater 
degree  of  refinement  of  knowledge  exists,  regarding  so  complete  a 
section  of  the  Devonian  or  any  other  Paleozoic  system  in  North 
America,  than  that  of  New  York  state. 

The  latest  classification  of  the  New  York  Devonian  system  by 
the  State  Geological  Survey  follows: 


Chautauquan  I  Chem        and  Catskill  sandstones, 
series  { 


UPPER  DEVONIAN    j  genecan  r  Portage  sandstones  and  shales, 

series  <  Genesee  shales. 

(  Tully  limestone. 

Erian  f  Hamilton  shales  and  limestone, 

series  \  Marcellus  shales  and  limestone. 

MIDDLE  DEVONIAN 

Ulsterian  f  Onondaga  limestone, 

series  \  Schoharie  grit. 

120 


THE  DEVONIAN  PERIOD 


121 


LOWER  DEVONIAN 


Oriskanlan 
series 


Helderbergian 
series 


f  Esopus  grit. 

Oriskany  sandstone  and  Glenerie  lime- 
stone. 

Connelly  conglomerate. 
Port  Ewen  limestone. 

Becraft  limestone. 
New  Scotland  limestone. 
Kalkberg  limestone. 
Coeymans  limestone. 


For  a  long  time  the  Helderbergian  series  was  placed  with  the 
Silurian  system,  but  on  the  basis  of  careful  study  of  its  fossils,  it  is 
now  generally  agreed  that  it  really  represents  the  lowest  portion  of 
the  Devonian  system.  This  is  a  good  example  of  the  difficulty  in 
drawing  the  line  between  two  systems  when  no  sharp  stratigraphic 
break  or  unconformity  exists. 

As  stated  in  connection  with  the  preceding  system,  so  here  the 
reader  should  know  that  in  many  parts  of  America  where  definite 
correlations  have  not  been  made,  local  subdivisions  or  stage  names 
are  employed,  and  also  that  the  lithologic  character  of  the  various 
stages  in  New  York  may  be  quite  different  from  those  in  other 
regions. 


DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  The  map  (Fig.  68)  gives  the  surface 
distribution  of  all  known  Devonian  rocks  in  North  America.  A 
comparison  with  the  Silurian  strata  map  (Fig.  59)  will  show  that, 
in  the  eastern  part  of  the  continent,  these  two  rock  systems  are 
very  similar  in  distribution,  though  the  Devonian  is  absent  from 
Newfoundland  and  is  of  much  larger  surface  extent  in  New  York. 
As  compared  with  the  Silurian  the  only  other  important  differ- 
ences are  the  much  larger  Devonian  area  in  the  Mackenzie  River 
region  and  the  much  smaller  areas  in  the  Arctic  Islands  region. 

It  should  again  be  borne  in  mind  that  these  surface  areas  of 
Devonian  rocks  fall  far  short  of  indicating  the  actual  former,  or 
even  present  extent  of  rocks  of  this  age,  because  considerable 
Devonian  rock  has  been  removed  by  erosion,  and  much  is  now 
buried  under  later  formations.  Thus  in  the  Appalachians  and 
the  mountains  of  the  western  United  States,  the  Devonian  strata 
have  been  highly  folded  with  others,  so  that  only  the  outcropping 


122  HISTORICAL  GEOLOGY 

edges  are  visible.  In  the  Mississippi  Basin,  where  the  strata  are 
essentially  horizontal,  deep  well  borings  have  proved  that  the 
Devonian  strata  are  extensively  distributed  under  cover  of  later 
rocks. 

Lower  Devonian  Rocks.  —  The  Helderbergian  series  is  very 
limited  in  its  distribution,  and  is  found  almost  wholly  in  eastern 
North  America  in  three  regions:  (1)  Maine,  eastern  Quebec, 
Nova  Scotia,  and  New  Brunswick;  (2)  the  northern  and  middle 
Appalachians;  and  (3)  in  the  lower  Mississippi  Valley  in  Oklahoma, 
southeastern  Missouri,  and  western  Tennessee  and  Kentucky. 
Limestone  almost  everywhere  makes  up  the  series  which  ranges 
in  thickness  up  to  600  feet.  In  the  West,  this  series  has  been  rec- 
ognized only  in  the  great  body  of  Paleozoic  limestone  in  Nevada. 
Rocks  of  this  age  are  also  known  on  Kennedy  Island  west  of 
northern  Greenland. 

The  Oriskanian  series  is  chiefly  represented  by  the  Oriskany 
sandstone,  the  other  members  of  the  series  being  only  of  mere 
local  importance.  The  Oriskany  formation  is  extensively  developed 
from  central  New  York  southward  through  the  Appalachian  region 
to  Alabama,  and  in  the  eastern  Mississippi  Valley.  Its  thickness 
varies  from  a  few  feet  in  New  York,  to  several  hundred  feet  in 
western  Maryland.  In  northern  Maine,  New  Brunswick,  and 
Nova  Scotia,  the  Oriskany  (much  of  it  limestone)  is  well  developed 
though  not  much  studied. 

Middle  Devonian  Rocks.  —  The  Ulsterian  rocks,  except  the 
Schoharie  grit  which  is  limited  to  eastern  New  York,  are  much 
more  extensive  than  the  Lower  Devonian. 

The  Onondaga  limestone  formation  extends  from  eastern  New 
York  and  Pennsylvania  westward  to  northern  Michigan  and  south- 
ern Illinois,  except  over  the  Cincinnati  anticline  area.  Its  entire 
absence  from  all  but  the  .northern  portion  of  the  Appalachians  is 
particularly  noteworthy.  Its  thickness  is  seldom  over  200  feet,  and 
it  is  often  largely  made  up  of  Corals,  as  for  example  at  the  Ohio 
River  rapids  near  Louisville.  In  northern  Maine,  New  Brunswick, 
and  Nova  Scotia,  the  Onondaga  limestone  is  widespread  and  appar- 
ently many  hundreds  of  feet  thick.  It  also  occurs  at  the  south  end 
of  Hudson  Bay.  In  most  of  the  Devonian  areas  of  western  North 
America  (see  Fig.  68) ,  the  Onondaga  formation  is  doubtless  present 
though  not  yet  carefully  studied. 

The  Erian  series,  represented  by  the  Hamilton  and  Marcellus 


THE  DEVONIAN  PERIOD 


123 


shales  and  limestones,  has  very  much  the  same  distribution  as  the 
Onondaga,  except  for  the  absence  of  Erian  from  the  south  end  of 


Fig.  68 

Map  showing  surface  distribution  (areas  of  outcrops)  of  Devonian  strata  in 
North  America.     (Modified  by  W.  J.  M.  after  Willis,  U.  S.  Geological 

Survey.) 

Hudson  Bay,  and  additional  Erian  areas  in  the  middle  Appala- 
chians, Iowa,  northern  Missouri,  and  just  west  of  Lake  Winnipeg. 
In  the  east,  shales  were  deposited,  attaining  a  thickness  of  1500 


124  HISTORICAL  GEOLOGY 

to  5000  feet  in  Pennsylvania,  while  in  the  upper  Mississippi  Basin, 
where  much  limestone  still  formed,  its  thickness  is  notably  less. 
A  good  idea  of  the  distribution  (surface  and  concealed)  of  the 
Middle  Devonian  rocks  is  afforded  by  noting  the  water  areas  on  the 
paleogeographic  map  (Fig.  70),  though  from  these  areas  some 
Devonian  strata  have  been  removed  by  erosion. 

Upper  Devonian  Rocks.  —  These  show  a  distribution  very 
similar  to  the  Middle  Devonian,  except  that  the  southern  Appa- 
lachians and  region  immediately  westward  also  contain  them. 
Leaving  out  the  area  of  Onondaga  at  the  south  end  of  Hudson  Bay, 
a  good  conception  of  the  distribution  of  the  Upper  Devonian  rocks 
may  be  gained  by  examining  the  map  (Fig.  68),  because  almost 
everywhere  that  any  Devonian  is  present,  the  Upper  Devonian 
also  occurs. 

The  Senecan  series,  except  for  the  comparatively  thin  and  local 
Tully  limestone,  consists  of  the  Genesee  shales,  and  Portage  sand- 
stones and  shales.  The  Genesee  ranges  in  thickness  from  a  few 
feet  in  western  New  York,  to  several  hundred  feet  in  central 
Pennsylvania,  while  the  Portage  is  over  1000  feet  thick  in  western 
New  York. 

The  Chautauquan  (Catskill 1  and  Chemung)  series  of  sandstones 
have  a  thickness  of  1000  to  1500  feet  in  western  New  York;  3000 
feet  in  eastern  New  York;  and  a  maximum  of  8000  feet  in  eastern 
Pennsylvania.  The  Catskill  was  quite  certainly  mostly  a  fresh  or 
brackish  water  deposit. 

In  the  Mississippi  Valley,  westward  from  New  York  and  the 
Appalachians,  the  Upper  Devonian  is  much  thinner;  subdivisions 
are  not  so  well  represented,  or  recognized;  and  the  New  York 
names  have  not  been  applied.  Also  in  western  America,  the  Upper 
Devonian  subdivisions  have  not  been  well  made  out. 

Comparison  of  Ordovician,  Silurian,  and  Devonian  Systems.  — 
Comparing  the  rocks  of  the  Ordovician,  Silurian,  and  Devonian, 
as  these  are  developed  in  the  Appalachian  and  adjoining  regions, 
a  certain  rhythmic  or  periodic  recurrence  of  events  may  be  dis- 
covered among  them.  Each  system  is  characterized  by  a  great 
and  very  widespread  limestone  formation,  the  Trenton,  Lockport- 
Guelph  (Niagara),  and  Onondaga,  respectively,  and  in  each  the 
limestone  is  succeeded  by  shales  or  other  clastic  rocks,  the  Utica 

1  The  Catskill  is  essentially  an  eastern  pha.ee  of  the  Chemung  in  New 
York. 


THE  DEVONIAN  PERIOD  125 

(and  Frankfort),  Salina,  and  (Marcellus  to)  Portage  (respectively), 
due  to  an  increase  of  terrigenous  material,  and  each  was  closed  by 
a  more  or  less  widespread  emergence  of  the  sea-bottom.  Each 
began  with  a  subsidence  which  gradually  extended  to  a  maximum 
at  the  time  when  the  great  limestone  was  formed.  The  parallel- 
isms are  not  exact,  but  they  are  certainly  suggestive."  1 

Thickness  of  the  Devonian.  —  In  the  northern  Appalachian 
Mountains  the  Devonian  system  attains  a  maximum  thickness  of 
some  14,000  or  15,000  feet.  In  New  York  state  the  system  has  a 
thickness  of  fully  4000  feet.  Over  much  of  the  upper  Mississippi 
Valley  the  thickness  is  generally  less  than  1000  feet,  though  rather 
locally,  in  Ohio,  a  thickness  of  fully  3000  feet  is  reached,  2600  feet 
of  this  being  Upper  Devonian  shales  practically  equivalent  to  the 
Portage  and  Chemung  beds  of  the  east.  In  Nevada  the  system 
appears  to  show  6000  feet  of  limestone  and  2000  feet  of  shale. 

Igneous  Rocks.  —  As  in  the  earlier  Paleozoic  periods,  evidences 
of  igneous  activity  in  the  Devonian  period  are  almost  lacking. 
Some  lava  sheets  in  New  Brunswick,  Nova  Scotia,  eastern  Quebec, 
and  northern  California,  appear  to  be  interbedded  with  Devonian 
shales.  These  occurrences  prove  at  least  some  volcanic  activity 
during  the  period. 

PHYSICAL  HISTORY 

Early  Devonian.  —  In  earliest  Devonian  (Helderberg)  time 
most  of  North  America  appears  to  have  been  dry  land.  Inspection 
of  the  Paleogeographic  map  (Fig.  69)  of  that  time  shows  that 
marine  waters  occupied  only  three  rather  limited  areas  in  the  east. 
These  were  Nova  Scotia-New  Brunswick;  the  northern  Appala- 
chian region  to  central  New  York;  and  a  portion  of  the  southern 
Mississippi  Basin.  Of  these  the  first  two  were  doubtless  connected 
with  the  Atlantic,  and  the  last  with  the  Gulf  Basin  as  the  map 
suggests.  These  three  submerged  areas  must  have  been  pretty 
freely  connected,  probably  along  the  Atlantic  Coast,  because  the 
faunas  are  so  similar.  Since  the  Helderberg  formation  is  chiefly 
limestone,  the  waters  were  clear  and  this  implies  no  adjacent  high 
lands,  or  at  least  no  rapid  erosion.  In  the  west  an  arm  of  the  sea 
must  have  reached  into  the  Nevada  Basin  as  proved  by  the 
Helderberg  limestone  there,  the  connection  with  the  Pacific  prob- 

1  W.  B.  Scott:  An  Introduction  to  Geology,  2nd  Ed.,  pp.  577-578. 


126 


HISTORICAL  GEOLOGY 


ably  having  been   across  California  as  suggested  by  the  later 
geographic  conditions  (see  Fig.  69). 

The  Oriskany  sea  was  more  widespread  and  covered  the  whole 
Appalachian  region  from  central  New  York  to  Alabama  and  west- 


Fig.  69 

Paleogeographic  map  of  North  America  during  early  Devonian 
time.  (From  Schuchert's  "Historical  Geology,"  courtesy 
of  John  Wiley  and  Sons.) 

ward  over  much  of  the  eastern  upper  Mississippi  Basin,  except 
probably  the  Cincinnati  anticline  area.  Nova  Scotia-New  Bruns- 
wick remained  submerged.  The  sharp  change  to  deposition  of 


MIDDLE  DEVONIAN 

NORTH    AMERICA 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAND 
LANDS 
INDETERMINATE  AREAS 

POLAR 


Fig.  70 

Paleogeographic   map   of   North   America   during   Middle   Devonian   time. 
(Slightly  modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology,} 


128  HISTORICAL  GEOLOGY 

coarse,  clastic  sediments  argues  for  considerable  land  rejuvenation, 
or  much  more  rapid  erosion,  or  both.  The  sediments  are  of  distinctly 
shallow-water  character,  and  the  fossils  show  the  fauna  to  have 
been  suited  to  such  conditions.  The  fossils  are  remarkably  similar 
to  those  of  the  same  age  (Coblenzian)  in  Europe  from  which  region 
they  appear  to  have  migrated.  "The  evidence  then  is  fairly 
conclusive  that  during  the  period  represented  by  the  Coblenzian 
Oriskany,  the  arenaceous  epicontinental  sediment  was  the  ground 
traversed  by  the  Coblenz  fauna  westward  along  the  North  Atlantic 
continent"  (J.  M.  Clarke).  In  other  words,  there  must  have  been 
a  land  connection  between  Europe  and  North  America. 

Middle  Devonian.  —  During  Ulsterian  time  (neglecting  the 
slight  deposition  of  Schoharie  grit  in  eastern  New  York)  important 
geographic  changes  took  place.  The  Appalachian  Basin  from 
Pennsylvania  southward  was  raised  into  land,  but  the  sea  con- 
tinued from  eastern  New  York  and  Pennsylvania  across  the  Upper 
Mississippi  Basin  to  northern  Michigan  and  southern  Illinois, 
except  probably  around  the  Cincinnati  anticline  area.  Much  of 
New  Brunswick  and  the  region  at  the  southern  end  of  Hudson  Bay 
were  submerged,  as  well  as  the  Rocky  Mountain  district  from 
Alaska  to  western  Colorado,  northern  Arizona,  and  Nevada. 
Marine  waters  covered  the  areas  much  as  shown  on  the  map 
(Fig.  70)  except  for  the  absence  of  the  sea  from  the  northern  Ap- 
palachian district  and  the  large  area  from  the  Mississippi  River  to 
the  Rocky  Mountains.  This  was  the  great  Onondaga  sea,  which 
must  have  been  mostly  clear,  shallow,  and  comparatively  warm  as 
indicated  by  the  widespread  accumulation  of  largely  coralline 
limestone  already  mentioned.  Evidently  there  were  no  rapidly 
eroding  land  areas. 

Late  middle  Devonian  (Erian)  time  witnessed  another  impor- 
tant physical  change  probably  due  to  a  very  considerable  rejuvena- 
tion of  northern  Appalachia,  resulting  in  renewed  erosion  and 
deposition  of  vast  quantities  of  muds  in  the  eastern  part  of  the 
interior  sea.  These  muds  are  now  hardened  and  called  the  Mar- 
cellus  and  Hamilton  shales.  Farther  westward  in  the  Mississippi 
Basin,  however,  much  limestone  still  formed  in  the  clearer  sea. 
The  relations  of  land  and  water  during  this  (Erian)  time  are  de- 
picted on  the  paleogeographic  map  (Fig.  70).  One  feature  to  be 
especially  noted  is  the  long,  narrow,  land-bridge  from  Wisconsin 
to  Texas,  separating  the  eastern  from  the  western  interior  seas. 


130  HISTORICAL  GEOLOGY 

The  eastern  interior  sea  was  probably  connected  with  the  Gulf 
on  the  south,  and  with  the  Atlantic,  through  the  St.  Lawrence 
Basin,  on  the  north. 

Late  Devonian.  —  During  late  Devonian  (Senecan  and  Chau- 
tauquan)  time  the  relations  of  land  and  water  were  much  the  same 
as  during  middle  Devonian,  with  the  following  principal  differences: 
The  eastern  and  western  interior  seas  became  connected;  the 
southern  Appalachian  region  became  submerged;  and  the  connec- 
tion with  the  Gulf  of  Mexico  appears  to  have  been  closed.  In 
New  York  and  the  northern  Appalachian  region,  there  was  a  tre- 
mendous accumulation  of  sandstone  together  with  more  or  less 
shale  and  conglomerate.  The  Chemung-Catskill  formation,  as 
already  stated,  is  largely  a  shallow-water,  non-marine  deposit  from 
1500  to  8000  feet  thick  in  New  York  and  Pennsylvania.  The  few 
known  fossils  are  non-marine  types.  This,  together  with  the 
common  occurrence  of  red  shales  and  sandstones,  and  the  great 
thickness  of  the  beds,  all  point  to  the  origin  of  this  remarkable 
formation  as  either  a  great  delta  deposit  pushed  out  into  the 
shallow  interior  sea,  or  as  an  estuarine  or  lagoon  deposit.  Notable 
thinning  toward  the  west  proves  the  material  to  have  come  from 
the  east,  doubtless  from  greatly  rejuvenated  Appalachia.  Farther 
westward,  over  Michigan,  Indiana,  and  Tennessee,  the  deposits 
formed  at  the  same  time  were  mostly  shales,  usually  not  over  a 
few  hundred  feet  thick. 

Close  of  the  Devonian.  —  Throughout  most  of  North  America 
there  was  a  quiet  transition  from  the  Devonian  to  the  succeeding 
Mississippian,  therefore  the  two  systems  are  not  sharply  separated. 
In  Maine,  Nova  Scotia,  and  New  Brunswick,  however,  the  strata 
were  considerably  upturned  and  eroded  toward  the  close  of  the 
Devonian,  and  Mississippian  rocks  rest  upon  them  by  unconformity. 


q^  PROTON 


Europe.  —  It  may  be  said  in  general  that  the  Devonian  of 
Europe  began  with  a  progressive  transgression  of  the  sea,  con- 
tinuing till  near  the  close  of  the  period  when  much  of  the  continent 
was  submerged  as  shown  in  Fig.  72.  This  extensive  sea  spread 
over  the  barrier  which,  since  Cambrian  time,  had  quite  effectually 
kept  Europe  divided  into  two  provinces  (a  northern  and  a  southern) 
or  basins  of  deposition. 


THE  DEVONIAN  PERIOD 


131 


In  the  southern  British  Isles  there  are  thick  marine  strata  con- 
taining much  contemporaneous  igneous  rock  (lava  sheets),  while  in 
the  northern  portion  occurs  the  famous  "Old  Red  Sandstone" 
which  is  largely  of  continental  origin.  This  sandstone  attains  a 
greatest  thickness  of  fully  20,000  feet,  of  which  6000  feet  are  inter- 
bedded  lavas  and  tuffs.  Deposition  of  the  sandstone  appears  to 
have  taken  place,  probably  partly  as  delta  and  partly  as  wind-blown 


Fig.  72 

Sketch  map  showing  the  general  relations  of  land  and  water  in  Europe  during 
the  Devonian.  Horizontal  lines  =  Early  Devonian;  vertical  lines  = 
additional  areas  of  Middle  Devonian.  (After  De  Lapparent,  from 
Chamberlin  and  Salisbury's  " Geology,"  courtesy  of  Henry  Holt  and 
Company.) 

deposits,  in  basins  or  lagoons  more  or  less  cut  off  from  the  open  sea, 
or  at  times  in  fresh-water  lakes.  Fossils  are  not  abundant,  but 
they  constitute  a  remarkable  assemblage  of  land,  fresh  water,  and 
marine  species  scattered  through  various  horizons.  In  many 


132  HISTORICAL  GEOLOGY 

respects  the  "  Old  Red  Sandstone  "  is  much  like  the  Chemung- 
Catskill  formation  of  America. 

The  typical  marine  strata  of  Germany  also  contain  many  beds 
of  lava,  thus  indicating  much  igneous  activity  during  the  period. 

In  west-central  Europe  much  of  the  Devonian  has  been  meta- 
morphosed. 

Typical  marine  limestones,  shales,  and  sandstones  were  exten- 
sively deposited  in  Spain,  France,  Switzerland,  much  of  Austria, 
and  Russia,  but  with  Lower  Devonian  mostly  absent  from  Russia. 
Coralline  limestones  are  prominent  in  the  Alps. 

Other  Continents.  —  The  Devonian  sea  spread  over  most  of 
Siberia  and  into  central  Asia  and  China.  Rocks  of  this  age  are 
also  known  in  various  parts  of  southern  Asia,  northern  and  south- 
ern Africa,  Australia,  New  Zealand,  and  in  South  America  they 
appear  to  be  more  widespread  than  the  rocks  of  any  other  Paleozoic 
system.  Most  of  South  America  must  have  been  submerged  under 
a  transgressing  sea. 

CLIMATE 

The  general  distribution  and  character  of  the  fossils,  as  for 
example  the  Corals  of  the  Onondaga  sea,  indicate  rather  mild  and 
uniform  climatic  conditions.  Possibly  such  red  formations  as  the 
Catskill  arid  the  "Old  Red  Sandstone"  were  formed  under  arid  or 
semi-arid  conditions.  What  appears  to  be  boulder  clay  with 
striated  pebbles,  implies  at  least  local  glaciation  in  South  Africa. 

ECONOMIC  PRODUCTS 

Oil  and  gas  are  principally  derived  from  Devonian  strata  in  the 
great  fields  of  western  Pennsylvania,  West  Virginia,  and  western 
New  York. 

Flagstones  of  Devonian  age  are  extensively  quarried  in  south- 
ern New  York  and  in  Pennsylvania. 

Black  phosphate  deposits  occur  in  the  Upper  Devonian  shales 
of  central  Tennessee. 

LIFE  OF  THE  DEVONIAN 

Plants.  —  Of  the  Algce,  both  Sea-weeds  and  Diatoms  are 
known  in  fossil  form,  though  they  are  not  abundant.  Certain 
forms  regarded  as  tree-like  Sea-weeds  were  remarkable  for  their 


THE  DEVONIAN  PERIOD  133 

size,  having  attained  a  diameter  of  two  or  three  feet.  Diatoms  are 
unicellular,  aquatic  plants  of  microscopic  size  which  secrete  shells 
of  silica,  and  some  of  Devonian  age  are  known.  In  some  of  the 
later  periods  these  tiny  plants  were  of  considerable  importance. 
No  Bryophytes  (Mosses)  have  yet  been  discovered.  Spores  and 
spore-cases  of  certain  aquatic  plants  (Rhizocarps),  probably  related 
to  very  simple  Pteridophytes,  are  very  abundant  in  the  black 
shales,  especially  those  of  Marcellus  and  Hamilton  ages.  Accord- 
ing to  Dawson  they  are  "  dispersed  in  countless  millions  of  tons 
through  the  Devonian  shales,"  and  by  their  decomposition  much 
oil  has  been  produced. 

Our  knowledge  of  land  plants  prior  to  the  Devonian  is  very 
scant  as  we  have  seen,  but  the  records  are  sufficient  to  make  it 
certain  that  the  Devonian  lands  were  covered  with  a  rich  and  diver- 
sified vegetation,  often  even  with  luxuriant  forests.  The  forests 
were,  however,  far  different  in  appearance  from  those  of  the  present 
because  the  trees  were  all  of  very  simple  or  low  organization  types. 
Thus  they  were  largely  represented  by  all  the  main  subdivisions 
of  the  non-flowering  Pteridophytes  such  as  Lycopods,  Equisetce, 
Ferns,  and  Seed-ferns,  and  some  simple  types  of  the  lower  order 
of  flowering  plants  (i.e.  Gymnosperms)  were  also  present.  Since 
these  important  and  remarkable  land  plants  reached  their  climax 
of  development  in  the  Pennsylvanian  (great  coal  period),  it  will 
serve  our  purpose  best  to  discuss  these  plants  in  connection  with 
the  flora  of  the  Pennsylvanian. 

Protozoans.  —  Foraminifers  and  Radiolarians  no  doubt  existed 
"because  they  are  known  from  the  immediately  preceding  and  suc- 
ceeding periods,  but  fossil  forms  have  not  been  found. 

Porifers.  —  Sponges  were  common  but  they  require  no  special 
description. 

Coelenterates.  —  The  Graptolites  which  are  so  abundant  and 
important  for  correlation  purposes  in  the  three  preceding  systems, 
are  comparatively  rare  in  the  Devonian,  and  they  became  almost 
extinct  before  the  close  of  the  period. 

Corals  displayed  a  very  marked  increase  in  numbers,  species, 
and  size.  They  must  have  grown  in  profusion,  especially  in  the 
clear  Onondaga  sea,  as  proved  by  the  many  great  fossil  Coral  reefs. 
From  near  Louisville,  Kentucky,  alone  more  than  200  species  are 
known,  and  these  are  only  a  fraction  of  all  described  Devonian 
species.  They  were  almost  all  of  the  cup  and  honeycomb  types, 


134 


HISTORICAL  GEOLOGY 


the  Chain  Corals  having  become  rare  and  extinct  in  the  early 
Devonian.  The  solitary  Cup  Corals  probably  reached  their  culmi- 
nation in  size,  some  of  them  being  12  to  18  inches  long  and  several 
inches  in  diameter. 

Echinoderms.  —  Cystoids  were  rare  and  became  extinct  during 
this  period.    Blastoids  still  continued   to  assume  a  minor  role. 


Fig.  73 

A  Devonian  Asterozoan,  Paleaster  eucharis,  on  a  Pelecypod  shell. 
•  (After  Clarke,  N.  Y.  State  Mus.  Bui.  158.} 

Crinoids  continued  to  increase  and  diversify.  Asterozoans  (Star- 
fishes) notably  increased  (Fig.  73),  while  the  Echinozoans  (e.g. 
Sea-urchins)  were  only  moderately  represented. 

Molluscoids.  —  Bryozoans  were  present,  but  not  conspicuous 
as  reef  builders. 

Brachiopods  reached  their  culmination  as  regards  numbers  of 
species  and  abundance  (Fig.  74).  Here,  as  in  the  three  preceding 
periods,  Brachiopods  were  the  most  numerous  fossils,  and  most 


THE  DEVONIAN  PERIOD 


135 


of  them  still  had  straight  hinge  lines.  Many  Spirifers,  particu- 
larly the  wide  " butterfly"  genera  (Fig.  74a)  were  common  and 
characteristic. 


b  d 

Fig.  74 

Devonian  Brachiopods:  a,  Spirifer  disjunctus;  b,  Spirifer  inter- 
medius;  c,  Stropheodonta  demissa;  d,  Productus  Hallanus.  (All  from 
Md.  Geol.  Survey,  "  Devonian.") 

Mollusks.  —  Pelecypods  and  Gastropods  were  much  like  those 
of  the  Silurian,  though  with  various  genera  and  species  changes 
(Figs.  75,  76). 

Among  the  chambered  Cephalopods,  a  significant  change  took 
place  with  the  introduction  of  the  Ammonoids  (e.g.  Goniatite, 
Fig.  77)  in  which  the  septa  or  partition  junctions  were  angular  or 
irregular  instead  of 
simple  or"  straight 
as  in  all  previous 
forms  (Nautiloids) . 
As  we  shall  see,  this 
irregularity  of  par- 
tition structure 
gradually  evolved 
into  more  and  more 
complex  forms, 


reaching  a  maxi- 
mum in  the  Meso- 
zoic  era.  (See  table 


Fig.  75 

Devonian  Pelecypods:  a,  Actinopteriate  textilis;  b, 
Grammysia  arcuata.  (From  Md.  Geol.  Survey, 
"Devonian.") 


136 


HISTORICAL  GEOLOGY 


on  page  99.)     Most  of  the  common  Nautiloid  types  still  persisted, 
though  the  simpler  forms   (straight  and  slightly   curved)   were 

notably  diminished  in 
prominence. 

Arthropods.  - 
Trilobites    showed     a 
marked   r|f>p,1inft_in 
numbers 


a  be 

Fig.  76 

Devonian  Gastropods:  a,  Platyceras  gebhardi; 
b,  Pleuromaria  capillaria;  c,  Loxonema  hamil- 
tonice.  (From  Md.  Geol.  Survey  "  Devonian.") 


tKough  they  were  not 
uncommon,  and  were 
still  often  fantastically 
decorated. 

Eucrustaceans  were 
fairly  represented  by 
several  types. 

Arachnids  were 
represented  by  Scor- 
pions and  Eurypterids,  and  the  Myriapods  made  their  first  known 
appearance.  Eurypterids  probably  culminated  in  the  preceding 
period,  but  they  were  still  prominent  and  notable  for  great  size, 
one  type  having  attained  a  length  of  eight 
feet. 

Insects  are  not  known  from  the  Devonian. 
Simplest  Vertebrates.  —  Perhaps  the 
most  interesting  and  important  feature  of 
Devonian  life  was  the  profusion  and  de- 
vjupm^nt  of  the  simple  Vertebrates,  par- 
ticularly the  Fishes.  These  simple  or  primi- 
tive Vertebrates  are  of  unusual  significance 
because  they  were  the  progenitors  of  the 
great  groups  of  higher  Vertebrates,  which 
gradually  became  more  complex  and  diversi- 
fied, and  finally  culminated  in  Man  him- 
self. All  known  Devonian  Vertebrates  were 
aquatic._ 

Paleospon4ylfls.  —  This  remarkable  creature  was  an  exceed- 
ingly simple  and  primitive  type  of  Vertebrate.  Its  appearance  is 
well  shown  in  Fig.  79.  The  animal,  one^or  two  inches  long, 
possessed  a  distinct,  a]  mi  Her,  segmented,  cartilaginous  vertebral 
cplwmn  supplied  at  one  end  with  a  rather  symmetrical  tail  fin 


Fig.  77 

A  Devonian  Goni- 
atite,  Manticoceras 
patersoni.  (After 
HaU.) 


THE   DEVONIAN  PERIOD 


137 


structure,  and  at  the  other  with  a  head.    The  head  had  a  circular 

mouth  but  no  jaws.  .  Its  lack  of  jaws  and  paired  fins  cause  it  to 

rank  below  the  true  Fishes, 

and  it  is  probably  to  be 

classed  with  the  Lamprey 

Eels. 

Ostracoderms. —  These 
curious  and  bizarre  forms 
also  represent  a  very  simple 
class  of  the  Vertebrates. 
For  a  long  time  they  were 
classed  as  simple  Fishes, 
but  recent  study  has  led 
some  to  believe  that  they 
are  really  transition  forms 
between  the  highest  inver- 
tebrates (Arthropods)  and 
the  Fishes  which  rank  very 
low  among  the  Vertebrates. 

A  characteristic  feature 
is  the  cover  orarmor  of 


a  b 

Fig.  78 

Devonian    Trilobites:     a,    Phacops    logani 
(Hall);    b,  Homalonotus  notions  (Clarke). 


bony  j)1a.tes  developed  in  the  skin  over  the  head  and  fore  part 
of  the  body,  hence  the  name,  which  literally  means  "shell-skin." 
The  rear  part  of  the  body  was  generally  covered  with  scales.  Some 


Fig.  79 

A  very  simple  Devonian  Vertebrate,  Paleospondylus  gunni. 
(After  Dean,  restored  by  Traquair,  from  Chamberlin  and 
Salisbury's  "Geology,"  courtesy  of  Henry  Holt  and  Com- 
pany.) 

had  vertebrated  tail  fins  and  were  fish-likejn_appearance  (Fig.  80a), 
while  others  looked  much  like  Tnlobites~or  King-crabs.  Some  had 
a  pair  of  jointed  flappers  or  swimming  paddles_£xtending  out  from 


138 


HISTORICAL  GEOLOGY 


the  fore  part  of  the  body,  but  none  had  true  paired  fins  like  the 
Fishes.  The  vertebral  column  was  of  cartilage  (gristle).  The  eyes 
were  close  together  near  the  top  of  the  head.  They  did  not  possess 
true  jaws  in  the  Vertebrate  sense  of  that  term,  but  rather  the  simple 

jaw-like  portions 
moved  over  each 
other  laterally 
as  in  many  Ar- 
thropods (e.g. 
Beetles). 

Ostracoderms 
reached  the 
zenith  of  their 
development 


in 

the  Djjvjinian, 
and,  so  far  as 
known,  they  hp- 
c  a  me  extinct 
during  the  same 
period. 

Fishes.— Be- 
cause of  the  pro- 
fusion of  Fishes, 
the  Devonian  is 
Fig.  80  often  called  the 

Devonian  Ostracoderms:  a,  Pterichthys  testudinarius,  "  Age  of  Fishes. " 
restored  (Dean  after  Woodward);  b,  Tremataspis,  Their  abundance 
restored  (after  Patten). 

together   with 

their  importance  as  bearing  upon  the  evolution  of  the  Verte- 
brates, requires  that  considerable  attention  be  devoted  to  the 
Fishes  here.  In  all  of  our  discussion  of  the  geological  history  of 
Fishes,  the  following  important  groups  only  will  be  recognized: 
(1)  Selachians  ("  Cartilage  "-fishes),  now  uncommon,  but  e.g. 
Sharks;  (2)  Dipnoans  ("  lung  "-fishes),  now  rare,  but  e.g.  Ceratodus 
of  Australian  rivers;  (3)  Arthrodirans  (e.g.  Fig.  82b),  now  wholly 
extinct;  (4)  Ganoids  ("  lustre  "-fishes),  now  uncommon,  but  e.g. 
Gar-pike  and  Sturgeon;  and  (5)  Teleosts  ("perfect  bone  "-fishes) , 
now  the  most  abundant  of  all  Fishes,  e.g.  Trout,  Salmon,  Cod. 

Selachians  are  the  simplest  of  all  true  Fishes,  and  they  comprise 
the  oldest  group  of  living  Fishes,  dating  back  at  least  to  the 


THE  DEVONIAN  PERIOD 


139 


Silurian.    Their  skeletons  are  wholly  cartilaginous,  the  only  hard 
parts  being  the  teeth  and  fin  spines  which  are  commonly  preserved 


Fig.  81 

A  Paleozoic  (early  Mississippian)  Selachian  or  Shark,  Cladoselache 
fyleri.     (Restored  by  Dean.) 

as  fossils.  The  arrangement  of  separate  gill  slits  in  the  throat 
wall  is  a  more  eel-like  than  fish-like  feature.  Simple,  paired  fins 
are  present,  but 
scales  or  plates 
are  absent.  They 
were  common  in 
the  Devonian 
seas,  and  also 
probably  in  lakes 
and  lagoons.  Fig. 
81  exhibits  a  typ- 
ical Paleozoic 
species  which  is 
very  similar  to 
living  forms. 

Dipnoans  are 
remarkable  in 
being  able  to 
breathe  both  in 
water  and  air, 
since  they  have 
both  gills  and 


Fig.  82 

Devonian  Fishes:  a,  Dipnoan,  Dipterus  valenciennesi, 
(restored  by  Traquair);  6,  Arthrodiran,  Coccosteus 
dedpiens  (restored  by  Woodward);  c,  Ganoid, 
Osteolepis  (restored  by  Nicholson). 


lungs,  the  air- 
bladder  being 
more  or  less  used 
as  a  lung.  They  were  abundant  during  Devonian  time.  Fig.  82a 
shows  a  common  Devonian  species  which  is  remarkably  similar 
to  the  modern  Ceratodus.  Note  the  paddle-shaped  paired  fins, 


140  HISTORICAL  GEOLOGY 

almost  like  legs,  and  the  covering  of  scales.  Their  skeletons  were 
cartilaginous.  Their  limb-like  fins  and  peculiar  lung-like  air  sacs 
were  more  amphibian-like  than  fish-like  characters  and  they 
strongly  suggest  that  the  Dipnoans  may  have  been  the  progenitors 
of  the  Amphibians. 

Arthrodirans  comprise  a  remarkable  group  of  Fishes  now  wholly 
extinct,  but  they  were  common  in  Devonian  time.  Fig.  82b 
shows  an  example  of  a  well-known  genus  (Coccosteus)  from  the 
Old  Red  Sandstone.  Note  the  bony  armor  covering  the  fore  part 
of  the  body,  thus  suggesting  the  Ostracoderms,  though  the  paired 
fins  and  true  jaws  supplied  with  teeth  place  them  with  the  Fishes. 
The  backbone  was  of  unsegmented  cartilage.  Other  forms  closely 
related  to  Coccosteus  were  remarkable  for  size,  some  having 
attained  lengths  up  to  20  or  25  feet.  Arthrodirans  were  probably 
the  most  formidable  denizens  of  the  Devonian  seas. 

Ganoids  were  the  most  highly  organized  and  abundant  Fishes 
of  the  time.  These  were  characterized  by  a  covering  of  small 

lustrous  plates  or  bony  scales,  usually 
rhomboid  and  set  together  like  tile, 
rather  than  by  overlapping  as  in  typ- 
ical modern  Fishes.  The  skeletons  were 
of  cartilage,  though  in  later  periods 
they  were  more  or  less  ossified  as  in 

the  few  modern  representatives.  Their 

Structure  of  a  Ganoid  tooth.      .    ,          i  ,      ,1  r,       -,   i 

/Af4.0-  A  „„««;„  >>  internal  tooth  structure  was  often  laby- 

^/\.I  lei     .T\.gd/»blA ,)  .,.,.  ,  -. 

rinthme  (Fig.  83)  or  much  like  that  of 

Amphibians  of  later  Paleozoic  periods.  A  typical  Devonian  Ganoid 
is  shown  in  Fig.  82c.  The  so-called  fringe-finned  Ganoids  were 
externally  rather  similar  to  the  Dipnoans,  especially  as  regards 
the  paired,  lobate,  limb-like  fins.  Their  intricate  (labyrinthine) 
tooth  structure,  character  of  the  skull  bones,  and  limb-like  fins, 
suggest  strong  affinities  with  the  Amphibians  of  the  later  Paleozoic. 

Teleosts,  which  are  the  most  common  and  typical  modern 
Fishes,  were  entirely  absent  from  the  Devonian.  In  these  the 
skeletons  are  completely  ossified  and  the  body  is  nearly  always 
covered  with  overlapping  scales.  In  marked  contrast  with  the 
Devonian  Fishes,  Teleosts  always  have  non-vertebrated  tail 
fins. 

General  Observations  on  Devonian  Fishes.  —  (1)  All  were  of 
simple  types.  The  most  typical  and  highly  organized  Fishes  so 


THE  DEVONIAN  PERIOD 


141 


common  today,  did  not  exist  in  the  Devonian,  and  even  the  Ganoids 
were  of  primitive  types. 

(2)  All  had  cartilaginous  skeletons.    The  vertebral  column  and 
other  portions  of  the  skeleton  were  not  ossified  (i.e.  changed  to 
bone). 
"(3)  All  had  vertebrated  tail  fins.     The  vertebral 


tended  through  the  tail  fin  and  gave  off  fin  rays  to  support  a  lobe 
above  and  below.  Sometimes 
this  tail  fin  was  symmetric  and 
sometimes  asymmetric.  The 
asymmetric  form  is  regarded 
as  the  more  primitive.  Most 
modern  Fishes  (Teleosts)  have 
non-vertebrated  tail  fins,  the 
fin  rays  being  sent  out  from  a 
plate  at  the  end  of  the  verte- 
bral column. 

(4)  They  were  generalized 
types.  "  Along  with  their  dis- 
tinctive fish-characters,  they 
combined  others  which  connect 
them  with  higher  Vertebrates, 
especially  Amphibians,  and  still 
others  which  are  found  in  the 
embryos  of  Teleosts.  The  most 
important  connecting  charac- 
ters .  .  .  are:  (a)  An  external 
protective  armor  of  thick  bony 
plates  or  scales,  such  as  were 
possessed  by  early  Amphibians, 
and  by  many  Reptiles  of  the 
present  time;  (b)  Large  conical 
teeth  channelled  at  the  base,  and  of  labyrinthine  structure  on  sec- 
tion. This  structure  was  very  marked  in  early  Amphibians;  (c)  A 
cellular  air-bladder  .  .  .  capable  of  being  used  to  some  extent 
as  a  lung;  (d)  In  many  cases  paired  fins  which  had  something 
like  jointed  legs  running  through  them;  (e)  The  Tail  fin  verte- 
brated as  in  Reptiles."1  The  most  prominent  embryonic  charac- 
ters were  the  cartilaginous  skeleton  found  only  in  the  embryonic 
1  J.  Le  Conte:  Elements  of  Geology,  p.  356. 


Fig.  84 

Types  of  Fish  tails:  a,  vertebrated 
symmetric;  b,  vertebrated  non- 
symmetric;  c,  non-vertebrated  sym- 
metric. (Redrawn  after  Le  Conte.) 


142  HISTORICAL  GEOLOGY 

stage  of  the  typical  modern  Fishes  (Teleosts) ,  and  the  vertebrated 
character  of  the  tail  fin,  the  tail  of  the  modern  Teleost  successively 
passing  from  the  asymmetric  vertebrated  stage,  to  symmetric  verte- 
brated, and  finally  to  symmetric  non- vertebrated  (Fig.  84). 

Generalized  or  synthetic  types,  so  well  illustrated  by  Devonian 
Fishes,  are  of  great  importance  in  considering  the  evolution  and 
geological  history  of  organisms. 

Amphibians.  —  Footprints,  considered  to  be  those  of  Amphib- 
ians, have  been  found  in  the  Upper  Devonian  strata  of  Pennsyl- 
vania, but  remains  or  impressions  of  the  animals  are  not  known. 
At  any  rate  it  seems  certain  that  terrestrial  Vertebrates  existed  as 
early  as  the  Devonian. 


CHAPTER  X 


THE    MISSISSIPPIAN    (LOWER    CARBONIFEROUS)    PERIOD 
ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

FORMERLY  the  Carboniferous  period  included  all  of  what,  in 
America  at  least,  we  now  call  the  Mississippian,  Pennsylvanian, 
and  Permian  periods.1  In  Europe  the  term  Carboniferous  is  still 
employed,  though  the  Permian  has  been  separated  from  it.  The 
name  "  Carboniferous "  was  given  about  one  hundred  years  ago 
because  it  was  supposed  that  workable  coal  beds  were  almost,  if 
not  wholly,  confined  to  that  system.  Although  workable  coal  beds 
are  known  to  occur  in  most  later  systems,  nevertheless  what  was 
long  known  as  Carboniferous,  particularly  that  portion  now  called 
Pennsylvanian,  does  contain  the  world's  greatest  coal  deposits. 
The  name  "  Mississippian "  was  given  because  of  important  out- 
crops of  its  formations  in  the  eastern  Mississippi  Basin,  especially 
along  the  river. 

Some  idea  of  the  system  in  three  well-known  regions  may  be 
gained  from  the  following  table: 


Mississippi  River  States 

Pennsylvania 

Maryland 

4.  Chester  or  Kaskaskia 

series     (Limestones, 

sandstones  and  shales). 

3.  Mauch  Chunk 

3.  St.  Louis  series 

2.  Mauch  Chunk 

(Shales). 

MISSISSIPPIAN 

(Limestones)  . 

(Shales) 

SYSTEM 

2.  Osage  or  Augusta  series 

2.  Greenbrier 

(Limestones  and  shales). 

(Limestone). 

1.  Kinderhook  or  Chouteau 

1.  Pocono 

1.  Pocono 

series      (Limestones, 

(Sandstone). 

(Sandstone). 

shales,  and  sandstones)  . 

1  In  its  geologic  folios  the  U.  S.  G.  S.  still  uses  the  term  Carboniferous. 

143 


144  HISTORICAL  GEOLOGY 

It  will  be  seen  that,  in  the  Appalachian  region,  the  rocks  are 
almost  wholly  clastic,  while  limestones  are  prominent  in  the  Missis- 
sippi River  region.  Also  the  system  in  the  east  has  not  been  so 
much  subdivided,  and  detailed  correlations  with  the  subdivisions 
farther  west  have  not  been  made.  Regarding  the  detailed  classifi- 
cation of  subdivisions  in  America,  much  difference  of  opinion  still 
exists,  and  more  or  less  local  names  are  used  in  different  regions. 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  The  accompanying  map  (Fig.  85) 
shows  the  surface  distribution  of  the  Mississippian  and  Pennsyl- 
vanian  rocks  together.  In  the  western  part  of  the  continent  these 
two  systems  have  not  yet  been  satisfactorily  separated,  hence  it 
is  impossible  to  delimit  them  separately  upon  the  map.  Also  it 
must  be  borne  in  mind  that  the  large  areas  in  British  Columbia 
and  Alaska  contain  considerable  amounts  of  other  Paleozoic  rock 
as  well  as  early  Mesozoic  rock,  though  the  Mississippian  and  Penn- 
sylvanian  are  abundantly  represented.  In  the  eastern  part  of  the 
continent,  the  two  systems  have  been  clearly  separated,  and  map 
Fig.  86  shows  the  surface  distribution  of  Mississippian  strata 
there.  A  comparison  with  the  Devonian  surface  distribution  map 
(Fig.  68)  shows  that  the  Mississippian  has  a  very  similar  distribu- 
tion in  eastern  North  America,  and  that  the  Mississippian  generally 
borders  the  Devonian  areas.  This  is  because  the  Devonian  usually 
passed  so  quietly  into  the  Mississippian  with  continuous  deposition. 
A  distribution  feature  of  special  importance  as  compared  with  the 
Ordovician  and  Silurian,  and  to  some  extent  with  the  Devonian, 
is  the  complete  absence  of  Mississippian  strata  from  all  of  northern 
North  America  east  of  the  Rocky  Mountains  except  around  the 
mouth  of  the  St.  Lawrence  River. 

In  the  Appalachians,  Rockies,  and  mountains  still  farther  west, 
the  outcropping  strata  form  long  and  short,  narrow  belts  because 
the  rocks  have  been  highly  folded  and  only  the  eroded  edges  of 
upturned  strata  are  visible  (Fig.  113).  The  eastern  Mississippi 
Basin  shows  a  different  type  of  distribution  because  the  rocks  are 
there  in  nearly  horizontal  position  and  outcrop  where  the  later 
(overlying)  Paleozoic  strata  have  been  removed  from  them  by 
erosion,  or  where  later  sediments  were  never  deposited  upon  them. 
The  character  of  the  rocks  and  distribution  of  outcrops,  supple- 


THE  MISSISSIPPIAN  PERIOD 


145 


mented  by  many  deep  well  sections,  proves  that  Mississippian 
strata  underlie  nearly  the  whole  Mississippi  Basin  except  the  Gulf 
border,  and  Wisconsin  and  Minnesota. 


Fig.  85 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Mississippian 
and  Pennsylvanian  strata  in  North  America.  The  areas  in  British  Columbia 
include  some  other  Paleozoic  rocks  as  well  as  some  early  Mesozoic  rocks. 
(By  W.  J.  M.,  data  from  Willis,  U.  S.  Geological  Survey.) 

Lower  Mississippian  Rocks  in  the  East.  —  The  Pocono  sand- 
stone, also  including  some  conglomerate,  shale,  and  thin  beds  of 
coal,  extends  from  northern  Pennsylvania  to  Virginia  in  the  Appala- 
chian district.  Its  thickness  varies  from  about  2000  feet  in  Penn- 
sylvania to  about  100  feet  in  the  south.  As  judged  by  numerous 
terrestrial  fossils,  the  Pocono  appears  not  to  be  a  typical  marine 


146 


HISTORICAL  GEOLOGY 


deposit.  Just  west  of  the  Appalachians  considerable  shale  is 
associated  with  the  sandstone  of  this  same  age,  while  in  the 
Mississippi  River  states  the  Lower  Mississippian  is  represented  by 
the  Kinderhook  and  Osage  series,  which  contain  much  limestone. 
The  Kinderhook  consists  of  sandstone,  shale,  and  limestone,  but 


Fig.  86 

Map  showing  the  surface  distribution  (areas  of  out- 
crops) of  Mississippian  strata  in  eastern  North 
America.  (Modified  by  W.  J.  M.  after  Willis,  U.  S. 
Geological  Survey,) 

varies  greatly  in  lithologic  character  from  place  to  place.  The 
Osage  series  directly  overlies  the  Kinderhook,  and  is  dominantly 
limestone,  though  with  some  shale.  Both  Kinderhook  and  Osage 
are  chiefly  true  marine  deposits.  Lower  Mississippian  strata  in 
southern  Michigan  are  mostly  sandstones  and  shales  (often  red), 
with  some  interbedded  salt  and  gypsum  deposits. 


THE  MISSISSIPPIAN  PERIOD  147 

Upper  Mississippian  Rocks  in  the  East.  —  In  the  northern 
Appalachian  district,  the  Mauch  Chunk  formation,  consisting 
mostly  of  red  sandy  shales,  directly  overlies  the  Pocono,  while  in 
Maryland  and  West  Virginia  the  lower  portion  of  the  Mauch 
Chunk  gives  way  to  the  Greenbrier  limestone.  The  Mauch  Chunk 
shows  a  maximum  thickness  of  3000  feet  in  eastern  Pennsylvania, 
but  this  diminishes  notably  to  the  north,  west,  and  south.  It  is 
considered  to  be  either  a  great  flood-plain  or  a  delta  deposit. 
Farther  west,  in  the  Mississippi  River  states,  the  Upper  Mississip- 
pian is  represented  by  the  Si.  Louis  and  Chester  series.  The 
former  is  made  up  almost  wholly  of  limestone  of  very  widespread 
extent,  while  the  latter  is  rather  variable  lit  biologically,  and  is 
more  restricted  in  distribution. 

The  Mississippian  of  Nova  Scotia  and  New  Brunswick  has  not 
been  so  carefully  subdivided,  but  it  is  largely  sandstone  below  and 
limestone,  with  some  red  beds  and  gypsum,  above.  Its  thickness 
is  about  2500  feet. 

Mississippian  of  the  West.  —  This  system  is  very  widely  dis- 
tributed in  the  West  as  proved  by  the  numerous  exposures,  but  it 
has  not  been  carefully  studied  and  subdivided  as  in  the  east. 
Throughout  the  system,  which  is  commonly  several  thousand  feet 
thick,  limestone  greatly  predominates.  Thus  in  the  Canadian 
Rockies  the  system  measures  over  6000  feet  thick  with  over  5000 
feet  of  limestone. 

Thickness  of  the  Mississippian.  —  The  Mississippian  system 
in  eastern  North  America  ranges  in  thickness  from  about  5000 
feet  in  eastern  Pennsylvania  to  only  some  hundreds  of  feet  in  the 
western  part  of  the  same  state. '  In  the  Mississippi  River  states  the 
maximum  thickness  is  1500  feet,  though  it  is  generally  less  than 
1000  feet.  In  the  western  part  of  the  continent  thicknesses  of 
several  thousand  feet  (maximum  over  6000  feet)  have  been 
observed  at  several  places,  while  in  other  localities,  as  in  the  Black 
Hills  and  parts  of  Colorado,  it  measures  only  a  few  hundred  feet 
thick.  Eighteen  hundred  feet  are  known  in  the  Grand  Canyon  of 
the  Colorado  River. 

Igneous  Rocks.  —  Igneous  activity  appears  to  have  been  wholly 
confined  to  the  region  from  Alaska  to  northern  California,  where 
vulcanism  occurred  on  a  large  scale.  Mississippian  rocks  are  there 
often  largely  made  up  of  igneous  materials. 


148  HISTORICAL  GEOLOGY 

PHYSICAL  HISTORY 

Earlier  Mississippian.  —  This  time  was  marked  by  a  still 
further  expansion  or  transgression  of  the  epicontinental  sea  which 
had  already  become  pretty  extensive  in  the  late  Devonian.  By 
the  close  of  the  Osage  epoch  of  the  Mississippian,  most  of  the  Mis- 
sissippi Basin  and  Appalachian  region,  as  well  as  much  of  the 
Rocky  Mountain  region,  had  become  submerged,  though  with 
considerable  islands  like  the  Cincinnati  anticline  area,  Ozark 
Mountain  area,  and  others  in  the  Rocky  Mountain  district. 
During  this  time  coarse,  clastic  sediment  (Pocono  sandstone) 
accumulated  along  the  western  shore  of  Appalachia;  red  beds,  with 
interbedded  salt  and  gypsum,  deposited  in  Michigan  in  lagoons 
bordering  the  Canadian  land;  and  chiefly  limestone,  with  some 
clastic  sediment,  were  laid  down  in  the  great  interior  sea. 

Later  Mississippian.  —  During  the  St.  Louis  epoch  the  Mis- 
sissippian sea  reached  its  maximum  extent,  when  even  the  islands 
of  the  Osage  epoch  were  submerged,  and  all  of  North  America  was 
covered  by  the  sea  except  the  northeastern  part  of  the  continent, 
Appalachia,  and  probably  some  lands  on  the  Pacific  Coast.  Map 
Fig.  87  shows  the  geography  of  the  continent  during  that  time. 
A  comparison  with  the  map  (Fig.  45)  of  the  mid-Ordovician  shows 
the  Ordovician  sea  to  have  been  more  interrupted  with  islands 
from  Appalachia  westward  across  the  continent  than  the  Missis- 
sippian (St.  Louis)  sea,  but,  because  of  the  extensive  arm  of  the 
Ordovician  sea  over  the  Hudson  Bay  region,  more  of  North  America 
was  then  submerged  than  during  the  Mississippian. 

In  the  east  vast  quantities  of  clastic  sediments  continued  to 
deposit  as  muds  (now  Mauch  Chunk  shales)  above  the  Pocono 
sands  along  the  western  shore  of  Appalachia.  Locally  conditions 
were  right  for  coal  formation  as  proved  by  some  coal  beds  in  the 
Mauch  Chunk.  The  interior  sea,  however,  had  clearer  waters 
than  at  any  time  since  the  Onondaga  epoch  of  the  Devonian,  and 
limestone  deposition  greatly  prevailed.  This  clear  sea  extended 
westward  even  across  the  site  of  the  Rocky  Mountains.  More 
red  beds  with  associated  salt  and  gypsum  continued  to  form  in 
southern  Michigan  lagoons.  Also  red  beds  and  gypsum  were 
formed  in  Nova  Scotia. 

Later  in  the  period  (Chester  epoch)  there  was  considerable 
withdrawing  and  shoaling  of  the  sea,  as  indicated  by  sandstones 


THE    MISSISSIPPIAN    PERIOD 


149 


MISSISSIPPIAN  i 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA,  MORE  LIKELY  LAND 
LANDS 

INDETERMINATE  AREAS 
MARINE  CURRENTS 


CONTINENTAL  DEPOSITS.  SOMETIMES 
NCLUDING  MARINE  SEDIMENTS 


Fig.  87 

Paleogeographic  map  of    North    America    in  Mississippian  time.   (Slightly 
modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.} 


150  HISTORICAL  GEOLOGY 

and  shales  which  make  up  a  good  percentage  of  the  rocks  along 
with  limestones.  Also  the  fact  that  the  rocks  of  the  Chester  series 
are  not  so  widespread  as  those  of  the  St.  Louis  proves  the  lesser 
extent  of  the  Chester  sea. 

Close  of  the  Mississippian.  —  A  significant  geographic  change 
marked  the  close  of  the  Mississippian  period.  Much,  if  not  practi- 
cally all,  of  the  great  area  covered  by  the  eastern  interior  sea  was 
converted  into  land  by  retrogression  of  the  sea.  Recent  studies  in 
the  western  part  of  the  continent  point  to  emergence  of  lands  in 
various  places  at  the  same  time,  though  the  extent  of  the  emergence 


M 


Fig.  88 

Generalized  section  in  Iowa,  showing  how  the  Pennsylvanian  system  (C) 
rests  unconformably  upon  the  Mississippian  (M).  (After  Keyes,  from  Cham- 
berlin  and  Salisbury's  "Geology,"  courtesy  of  Henry  Holt  and  Company.) 

there  is  not  so  well  known.  This  extensive  emergence  was  largely 
accomplished  without  very  appreciable  folding  or  tilting  of  the 
strata,  though  in  some  regions  moderate  folding  or  tilting  did 
occur,  as  in  Iowa  (Fig.  88),  Arbuckle  Mountains  of  Oklahoma, 
and  northeastern  Pennsylvania.  The  newly  exposed  lands  were 
notably  eroded,  and  the  Mississippian  and  Pennsylvanian  systems 
are  separated  by  one  of  the  most  extensive  and  distinct  uncon- 
formities in  the  whole  Paleozoic  group  of  rocks.  For  this  reason  the 
Mississippian  and  Pennsylvanian  should  be  regarded  as  separate 
systems  rather  than  as  merely  subdivisions  of  the  old  Car- 
boniferous. 

Comparisons  with  Preceding  Systems. — The  comparison  of  the 
Ordovician,  Silurian,  and  Devonian  systems  given  in  the  preceding 
chapter  (page  124)  to  show  a  certain  rhythmic  recurrence  of  events 
might  also  fairly  include  the  Mississippian,  because  this  period, 
like  the  others,  began  with  a  sea  transgression  which  reached  a 
maximum  (accompanied  by  much  limestone  making)  about  the 


THE  MISSISSIPPIAN   PERIOD  151 

middle  of  the  period,  followed  by  widespread  withdrawal  and  shoal- 
ing of  the  sea,  and  deposition  of  clastic  sediments  toward  the  close 
of  the  period. 

FOREIGN  (LOWER  CARBONIFEROUS)  MISSISSIPPIAN  l 

Europe.  —  As  in  North  America,  there  was  considerable 
encroachment  of  the  sea  so  that  much  of  the  non-marine  Old  Red 
Sandstone  became  covered  with  true  marine  sediments.  Map 


Fig.  89 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  during 
Mississippian  (Lower  Carboniferous)  time.  (Slightly  modified  after 
De  Lapparent.) 

Fig.  89  gives  a  general  idea  of  the  relations  of  land  and  water  in 
Europe  in  early  Mississippian  time.  In  western  Europe  limestone 
predominates.  Marine  waters,  mostly  free  from  land-derived 
sediments,  extended  from  the  western  British  Isles  to  central 

1  It  should  be  remembered  that  the  term  "Mississippian"  is  not  used  in 
Europe. 


152  HISTORICAL  GEOLOGY 

Germany.  In  these  waters  there  lived  vast  numbers  of  organisms 
such  as  Crinoids,  Corals,  etc.,  the  remains  of  which  accumulated 
to  build  a  great  mass  of  limestone  said  to  attain  a  thickness  of 
6000  feet  in  England,  and  over  2000  feet  in  Belgium.  Farther 
eastward,  in  central  Europe,  shales  and  sandstones  were  laid  down. 
In  Scotland  and  southern  England  also  shallow  water  deposits 
were  formed.  Throughout  much  of  central,  southern,  and  eastern 
Russia,  chiefly  non-marine  materials  were  deposited  as  proved  by 
the  many  coal  beds  and  associated  deposits.  The  rocks  of  Missis- 
sippian  age  in  southern  Europe  are  much  like  those  of  central 
Europe,  and  also  the  similarity  of  fossils  shows  that  northern  and 
southern  Europe  were  not  separate  provinces  as  during  most  of 
earlier  Paleozoic  time. 

Rather  widespread  crustal  disturbances  marked  the  close  of 
the  period  in  western  Europe.  As  a  result  of  the  upturning  and 
folding  of  the  rocks,  great  mountains  were  formed  principally  as 
two  chains  —  one  extending  from  Ireland  to  central  Germany,  and 
the  other  from  Bohemia  to  southern  France.  The  structure  of  the 
remnants  of  these  mountains,  as  seen  in  the  Vosges,  Harz,  Black 
Forest,  and  Cornwall  hills  or  low  mountains,  implies  deformation 
intense  enough  to  have  produced  high  altitudes.  Accompanying 
this  deformation  there  were  abundant  intrusions  and  extrusions  of 
igneous  rocks.  In  many  other  parts  of  Europe  there  were  relative 
changes  of  level  between  land  and  sea  without  very  appreciable 
folding  or  tilting  of  the  strata.  Thus,  the  reason  for  separating  the 
old  Carboniferous  into  two  systems  applies  with  great  force  to 
Europe  as  well  as  to  North  America. 

Other  Countries.  —  In  South  America  .  Mississippian  rocks 
are  known  in  Argentina  where  they  contain  some  coal,  in  Chili, 
and  in  other  parts  of  the  continent  where  they  have  not  been  care- 
fully separated  from  the  Pennsylvanian  (Upper  Carboniferous) . 

Eastern  Australia,  New  Zealand,  and  Tasmania  contain  marine 
strata  of  Mississippian  age  which  were  generally  highly  deformed 
toward  the  close  of  the  period,  and  injected  with  igneous  rocks. 
Salt  and  gypsum  occur  in  the  system  in  western  Australia. 

In  northern  Africa  the  system  is  extensively  represented, 
especially  by  limestone.  Non-marine  formations  occur  in  southern 
Africa. 

Rocks  of  Mississippian  age  are  also  known  to  be  widely  devel- 
oped in  Asia. 


THE  MISSISSIPPIAN  PERIOD  153 

CLIMATE 

As  for  the  earlier  Paleozoic  periods,  the  character  and  distri- 
bution of  Mississippian  fossils  pretty  clearly  prove  absence  of 
climatic  zones  like  those  of  today.  A  mild,  uniform  climate  ap- 
pears to  have  prevailed.  Salt  and  gypsum  beds  more  or  less 
associated  with  red  beds  point  to  arid  climate  in  Michigan, 
Montana,  Nova  Scotia,  and  Australia,  but  these  were  probably 
local  conditions.  Evidence  of  glaciation  toward  the  close  of  the 
period  has  been  reported  from  Oklahoma. 

ECONOMIC  PRODUCTS 

Much  oil  is  obtained  from  Mississippian  sandstones  in  western 
Pennsylvania,  West  Virginia,  Illinois,  and  Oklahoma. 

Some  gas  is  obtained  from  the  Chester  sandstone  of  Illinois, 
and  some  coal  from  the  Pocono  sandstone  of  West  Virginia. 

Building  stones  of  Mississippian  age  are  considerably  quarried, 
especially  the  oolitic  Bedford  limestone  of  Indiana,  which  is  per- 
haps the  most  widely  used  limestone  for  building  stone  in  the 
United  States. 

Vast  quantities  of  salt  are  produced  by  pumping  out  and  evap- 
orating the  natural  brines  from  the  Mississippian  sandstones  of 
Michigan,  and  smaller  quantities  from  the  sandstones,  or  lime- 
stones of  Ohio,  West  Virginia,  and  Virginia. 

Certain  important  zinc  ore  deposits  occur  in  the  Lower  Missis- 
sippian limestones  of  Missouri  and  Kansas  though  the  deposition 
of  the  ore  was  post-Mississippian. 

LIFE  OF  THE  MISSISSIPPIAN 

Plants.  —  In  general  the  flora  of  the  Mississippian  may  be 
said  to  have  been  very  much  like  that  of  the  Devonian,  though 
the  former  showed  greater  diversity  and  various  minor  changes. 
Because  of  the  prevalence  of  marine  waters  during  much  of  the 
time,  the  records  of  land  plants  are  perhaps  not  as  full  as  those  of 
the  preceding  period.  Fossil  plants  are  most  numerous  in  early 
Mississippian  rocks. 

The  simplest  plants,  such  as  Thallophytes  and  Bryophytes, 
were  present  but  their  fossil  forms  are  not  known  to  be  common. 


154 


HISTORICAL  GEOLOGY 


The  flora  of  the  period  consists  almost  entirely  of  the  highest 
Cryptogams  (i.e.  Pteridophytes)  and  the  simpler  Phanerogams 
(i.e.  Gymnosperms) .  As  in  the  Devonian,  all  the  .principal  groups 
of  the  Pteridophytes  —  Lycopods,  Equisetce,  and  Ferns  —  as  well 
as  the  still  higher  Seed-ferns  and  simpler  types  of  Gymnosperms 
were  represented.  All  of  these  plant  types  are  of  unusual  interest 
and  importance  but,  because  of  their  vastly  greater  abundance 


Fig.  90 

Mississippian  Cup-corals,  Lonsdaleia  canadense',  forming  a  compact  mass  or 
colony.     (After  Ulrich,  U.  S.  Geological  Survey,  Folio  95.) 

and  better  state  of  preservation  in  the  Pennsylvanian  rocks,  it 
will  be  best  to  postpone  their  somewhat  detailed  discussion  to  the 
next  chapter. 

Protozoans.  —  Foraminifers.  were  exceedingly  abundant,  es- 
pecially in  the  Mid-Mississippian  (St.  Louis)  sea.  The  famous 
Bedford  limestone  .of  Indiana,  for  example,  is  very  largely  made  up 
of  the  tiny  calcareous  shells  of  these  Protozoans.  Radiolarian 
(siliceous)  shells  are  very  abundant  in  some  formations  where 
they  make  up  layers  of  chert. 


THE  MISSISSIPPIAN  PERIOD 


155 


Fig.  91 
A  Mississip- 
pian  Blas- 
toid  head, 
Pentrim- 
ites  elon- 
gatus.  (Af- 
ter Shu- 
mard.) 


Porifers.  —  Sponges  continued  to  be  common. 
Coelenterates. — Graptolites  were  very  rare  and    became  ex- 
tinct.   Corals  showed  a  notable  decline  as  compared  with  their 
remarkable  development  in  the  Devonian,  though 
Cup-corals  especially  were  locally  numerous  in  the 
Mississippian  seas  (Fig.  90). 

Echinqderms.  —  Cystoids  were  absent,  having  be- 
come extinct  in  the  Devonian. 

Blastoids,  which,  during  several  preceding  periods, 
assumed  a  minor  role,  showed  a  wonderful  develop- 
ment in  the  Mississippian  when  they  appear  to  have 
reached  their  culmination  both  as  regards  numbers 
of  individuals  and  diversity  of  forms.  Fig.  91  shows 
one  of  the  most  common  types,  known  as  Pentremi- 
tes,  which  largely  constitutes  beds  of  limestone  in 
some  places.  At  certain  localities  even  the  most 
delicate  of  the  hard  parts  of  the  organisms  are  nearly 
. . . , ,  .  <  .  perfectly  preserved.  It  is  a 

remarkable  fact  that  this 
class  of  animals,  which  attained  such 
prominence  during  this  period,  also  be- 
came nearly  extinct  by  the  close  of  the 
same  period. 

Crinoids  also  culminated  during  this 
period.  Hundreds  of  species  are  known, 
and  some  localities  such  as  Crawfords- 
ville,  Indiana,  and  Burlington,  Iowa,  are 
well  known  for  the  remarkable  preserva- 
tion of  vast  numbers  of  these  beautiful 
forms  (fossil  " sea-lilies ").  "The  Crinoid 
remains  occur  in  such  multitudes  that  in 
many  places  the  limestones  are  principally  composed  of  them;  in 
such  places  they  must  have  covered  the  sea-bottom  like  miniature 
forests"  (W.  B.  Scott).  It  is  noteworthy  that  all  of  this  wealth 
of  forms  belonged  to  a  single  subclass  or  order  of  Crinoids  (Fig. 
92),  not  one  of  which  is  known  to  have  lived  on  into  the  Mesozoic. 
"The  rapid  decline  (of  Crinoids)  after  this  epoch  (Osage)  is  one  of 
the  most  remarkable  incidents  in  the  life-history  of  the  inverte- 
brates. .  .  .  The  ornamentation  of  the  Crinoids  at  this  time  was 
notable,  and  as  in  the  case  of  the  Trilobites,  preceded  the  decline 


Fig.  92 

A  Mississippian  Crinoid 
head,  Forbesiocrinus 
wortheni.  (After  Hall.) 


156  HISTORICAL  GEOLOGY 

of  the  group.  The  repetition  of  this  singular  phenomenon  at  dif- 
ferent times,  and  in  quite  different  groups  of  organisms,  is  worthy 
of  notice,  though  its  meaning  is  not  altogether  clear."  1 

Asterozoans  are  not  known  to  have  been  common. 

Echinoids  considerably  increased  in  numbers,  size,  and  diversity, 
and,  as  in  the  preceding  period,  all  belonged  to  a  now  extinct 
subclass. 

Molluscoids.  —  Bryozoans,  in  marked  contrast  with  the  Devo- 
nian, were  very  abundant,  and  in  some  cases  the  calcareous  skele- 
tons of  the  colonies  contributed  much  material  to  the  building  of 
limestone.  For  the  first  time  the  delicate  moss-like  colony  supports 
were  partly  replaced  by  thicker  and  heavier  supports,  a  good 
example  being  called  Archimedes  because  of  some  resemblance 
to  the  familiar  screw  of  the  same  name. 

Brachiopods  in  general  diminished  notably,  though  they  were 
by  no  means  uncommon.  Certain  important  earlier  Paleozoic 
genera  (e.g.  Pentamerus)  were  entirely  gone.  The  important 
genus  Spirifer  greatly  diminished  in  numbers  and  size  of  indi- 
viduals. Perhaps  the  most  important  Mississippian  genus  was 
Productus  with  many  species  and  some  of  the  largest  known 
individual  Brachiopods.  Straight-hinge  line  types  still  prevailed. 

A  very  fine  illustration  of  the  production  of  a  dwarfed  fauna  due 
to  unfavorable  environmental  influences  is  afforded  by  the  diminu- 
tive Brachiopods  and  associated  shells  of  the  Bedford  limestone 
of  Indiana.  Since  the  species  of  these  dwarfed  forms  are  the  same 
as  those  which  grew  to  normal  size  elsewhere,  it  is  evident  that  they 
must  have  lived  in  an  unfavorable  environment. 

Mollusks.  —  Pelecypods  were  more  common  than  ever  before, 
and  for  the  first  time  they  appear  to  have  been  more  numerous 
than  the  Brachiopods.  The  genera  were  much  like  those  of  the 
Devonian. 

Gastropods  continued  to  be  common  with  most  of  the  prominent 
Silurian  and  Devonian  genera  still  present. 

Cephalopods  were  much  like  those  of  the  Devonian.  All 
common  groups  of  Nautiloids  persisted  but  with  the  simpler  forms 
still  more  diminished.  The  coiled  forms,  however,  probably 
reached  their  climax  of  development  both  as  regards  numbers  and 
diversity  of  forms.  The  Ammonoids  were  still  represented  by  the 
Goniatites,  though  the  sutures  were  appreciably  more  complex 
1  Chamberlin  and  Salisbury:  College  Geology,  pp.  607-609. 


THE  MISSISSIPPIAN  PERIOD  157 

in  accordance  with  the  evolutionary  principle  already  given  in 
connection  with  this  group  (see  page  99). 

Arthropods.  —  Among  Crustaceans,  the  Trilobites,  which  were 
approaching  the  period  of  their  extinction,  were  few  in  number, 
comparatively  small,  and  usually  not  highly  decorated.  Eucrus- 
taceans  must  have  been  present  but  the  records  are  scant. 

Among  Arachnids,  the  remarkable  group  of  Eurypterids  had 
notably  fallen  off  both  in  numbers  and  size  as  compared  with 
the  Devonian. 

Myriapods  must  also  have  been  present  because  of  their 
existence  in  the  Devonian  and  their  abundance  in  the  succeeding 
Pennsylvanian,  but  fossil  forms  in  the  Mississippian  are  relatively 
scant. 

Fossil  Insects  are  not  known  from  the  Mississippian. 

Vertebrates. — Ostracoderms  became  extinct  with  the  Devonian. 

Fishes.  —  The  Selachians  (Sharks),  as  compared  with  the 
Devonian,  showed  an  extraordinary  development  in  numbers  and 
species.  They  were  doubtless  the  most  prominent  of  all  Fishes 
of  the  time,  many  hundreds  of  species  being  known.  Teeth  and 
spines  are  the  most  numerous  fossils.  In  sharp  contrast  with 
most  modern  forms,  many  species  had  the  mouths  lined  or  paved 
with  rough  plate-like  teeth  probably  suitable  for  grinding  such 
shelled  animals  as  Brachiopods,  Pelecypods,  etc.  The  spines 
were  doubtless  provided  for  defence  against  more  predaceous 
Fishes.  Dipnoans  and  Arthrodirans  still  continued  though  notably 
diminished.  Ganoids  were  still  prominent,  probably  having  been 
more  abundant  than  in  the  Devonian,  with  many  new  genera 
and  species. 

Amphibians.  —  As  we  have  learned,  there  is  good  reason  to 
think  that  Amphibians  lived  in  Devonian  time,  though  actual 
remains  are  not  known.  In  the  Mississippian  rocks  of  Scotland 
good  specimens  of  Amphibians  have  been  found.  These  all 
belong  to  the  long  extinct  and  remarkable  group  of  Stego- 
cephalians  which  will  be  described  in  the  next  chapter  because  of 
their  much  more  satisfactory  preservation  in  the  Pennsylvanian 
rocks.  As  already  suggested  in  our  discussion  of  Devonian  Fishes, 
it  is  well-nigh  certain  that  the  earliest  Amphibians  were  derived 
from  certain  types  of  Fishes  (Dipnoans).  In  fact  the  larval  forms 
of  Amphibians  are  true  water  animals  breathing  through  gills  and 
swimming  like  Fishes. 


CHAPTER  XI 
THE    PENNSYLVANIAN    (UPPER    CARBONIFEROUS)    PERIOD 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

As  stated  in  the  preceding  chapter,  the  Pennsylvanian  system 
represents  a  part  of  what  was  formerly  known  as  the  Carboniferous 
system  in  America.  In  other  continents,  strata  equivalent  to  the 
Pennsylvanian  are  usually  called  Upper  Carboniferous.  Rocks  of 
Pennsylvanian  age  include  the  Coal  Measures  proper  of  the  old 
Carboniferous,  and  they  contain  a  far  greater  supply  of  workable 
coal  than  the  rocks  of  any  other  system.  The  name  has  been  given 
because  of  the  typical  development  of  the  system  with  its  coal  in 
Pennsylvania  where  it  shows  the  following  subdivisions  generally 
recognized  in  the  eastern  United  States: 

4.  Monongahela  series  (Upper  Productive  Coal  Measures) 
(Shales,  sandstones,  and  limestones  with  much  coal). 

3.  Conemaugh  series  (Lower  Barren  Coal  Measures) 

(Sandstones,    conglomerates,    shales,  .  and   limestones 
with  some  coal). 


PENNSYLVANIAN 

SYSTEM 


Allegheny   series    (Lower   Productive    Coal    Measures) 
-     (Sandstones,  shales,  and   limestones  with  much  coal 

and  iron  ore). 
Pottsville  series 

(Sandstones  and  conglomerates  with  some  clays,  lime- 
stones, and  coal). 

In  the  interior  of  the  United  States  these  four  subdivisions 
have  scarcely  been  recognized  as  such.  For  example,  in  Iowa  the 
whole  system  is  divided  into  two  series:  (1)  Des  Moines  and  (2) 
Missourian.  Local  names  are  often  employed  in  other  portions  of 
the  Mississippi  Basin.  In  the  western  United  States  little  has 
been  done  toward  subdividing  the  system. 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  Only  in  the  eastern  part  of  the  con- 
tinent have  the  Mississippian  and  Pennsylvanian  rocks  been 

158 


THE  PENNSYLVANIAN  PERIOD 


159 


satisfactorily  separated.  The  accompanying  map  (Fig.  93) 
shows  the  surface  distribution  of  the  Pennsylvanian  in  eastern 
North  America.  Two  points  of  difference  as  compared  with  the 
older  systems  in  this  portion  of  the  continent  are  worthy  of  mention 
as  follows:  (1)  The  Pennsylvanian  rocks  occupy  distinctly  larger 


Fig.  93 

Map  showing  the  surface  distribution  (areas  of  outcrops) 
of  Pennsylvanian  rocks  in  eastern  North  America. 
These  are  also  essentially  the  great  areas  of  Penn- 
sylvanian coal.  (By  W.  J.  M.,  data  after  Willis,  U.  S. 
Geological  Survey.) 

(surface)  areas  than  the  rocks  of  any  older  Paleozoic  system,  and 
(2)  "the  commonest  position  for  the  outcrops  of  the  preceding 
Paleozoic  systems  severally  is  around  the  outcrops  of  the  older  sys- 
tems. But  the  outcrops  of  the  Pennsylvanian  exhibit  no  tendency 
to  a  similar  concentric  distribution.  Rather  do  they  seem  to  cover 
areas  between  the  outcrops  of  the  older  systems"  (Chamberlin 


160 


HISTORICAL  GEOLOGY 


i5    f&qA/ouj/omsl 
\paqioajucisasl 
>  paq  u/ejuno#wng 


CJ    0> 

"o  '3 


3  s- 


II 


O     02 


II 


o 

1 

* 


and  Salisbury).  The  reason 
for  such  differences  is  not  far 
to  seek.  For  instance,  Ordo- 
vician  rocks  are  actually  more 
widespread  than  the  Pennsyl- 
vanian, but  they  are  largely 
concealed  under  later  rocks, 
while  the  Pennsylvanian  rocks 
were  never  extensively  cov- 
ered by  later  deposits  (except 
Glacial  drift  and  to  a  small 
extent  by  Permian  strata 
in  the  Appalachian  district). 
Shortly  after  their  deposition, 
toward  the  close  of  the  Pale- 
ozoic, the  region  was  elevated 
and  has  remained  a  land  area 
ever  since.  Post-Paleozoic 
erosion  has  been  sufficient  to 
remove  much  of  the  Permian 
and  some  of  the  Pennsylva- 
nian, though  large  areas  of 
the  latter  rocks  still  remain  as 
shown  on  the  accompanying 
map. 

Pennsylvanian  rocks  are 
extensively  developed  in  the 
western  United  States  except 
in  Montana,  Idaho,  Washing- 
ton, and  Oregon.  They  prob- 
ably underlie  much  of  the 
Great  Plains  just  east  of  the 
Rockies  from  Wyoming  to 
Texas.  They  are  also  pretty 
widespread  in  Alaska. 

In  the  Appalachians  (Fig. 
94),  Nova  Scotia,  and  New 
Brunswick,  and  in  the  moun- 
tains of  the  west,  the  rocks  are 
highly  folded  or  tilted,  but 


THE  PENNSYLVANIAN  PERIOD  161 

in  the  Mississippi  Basin  they  have  remained  in  almost  horizontal 
position. 

Pennsylvania!!  Rocks  in  the  East.  —  Rocks  comprising  this 
system  in  the  eastern  part  of  North  America  are  partly  of  marine 
and  partly  of  non-marine  origin  with  the  latter  (including  coal) 
unusually  prominently  developed. 

The  following  extracts  from  a  paper  by  D.  White  concisely 
describe  the  Pennsylvanian  rocks  of  the  Appalachian  province 
(also  see  Fig.  95) :  "The  Pottsville,  like  the  succeeding  formations, 
is  composed  of  sandstones,  shales,  and  clays  (including  fire  clays, 
coals,  and  limestones),  but  it  contains  a  larger  proportion  of  sand- 
stones and  arenaceous  shales  than  the  later  formations  .  .  .  The 
Pottsville  is  thickest  in  the  southern  exposures,  where,  near  the 
eastern  outcrops,  it  probably  exceeds  7500  feet.  In  the  north- 
western bituminous  area  ...  it  measures  locally  less  than  200 
feet.  .  .  .  The  Pottsville  contains  all  the  workable  coals  south  of 
the  Kentucky-Tennessee  state  line. 

The  Allegheny,  next  succeeding  the  Pottsville,  is  a  thin  forma- 
tion characterized  by  a  larger  proportion  of  coal,  shale,  limestone, 
and  iron  ore.  In  the  bituminous  districts  .  .  .  the  Allegheny 
ranges  generally  between  250  and  350  feet  in  thickness  near 
the  northern  outcrop,  though  it  thins  southwestward  to  160  feet 
in  northeastern  Kentucky. 

The  Conemaugh,  which  succeeds  the  Allegheny,  is  generally 
marked  at  its  base  by  sandstone  or  conglomerate.  It  is  especially 
characterized  by  sandstones,  shales,  and  limestones,  intermingled, 
particularly  in  the  western  area,  with  red  and  green  shales,  clays, 
and  sandstones.  It  contains  less  coal  than  any  of  the  other 
Pennsylvanian  formations  of  the  Appalachian  trough.1 

The  Monongahela  is  distinguished  by  its  relatively  large  pro- 
portion of  coal  and  limestone,  the  latter  composing  over  one- 
third  in  some  districts.  The  formation  .  .  .  averages  about  325 
feet  or  less  in  thickness.  Its  coals,  including  the  great  Pittsburg 
coal  at  its  base,  are  of  notable  thickness  and  value."  2 

The  four  distinct  subdivisions  of  the  system  above  described 
are  generally  not  recognized  as  such  in  the  Mississippi  Basin,  but 
various  local  names  are  there  given  to  the  subdivisions  of  the 

1  A  maximum  thickness  of  800  to  900  feet  for  the  Conemaugh  is  shown  in 
western  Pennsylvania  and  Maryland. 

2  D.  White:  U.  S.  G.  S.,  Professional  Paper  71,  pp.  431-432. 


System 


- 

s  &. 
3 -a 


Kind  of  Rock 


Dunkard 

sandstone, 

limestone 

and  coal 


Monongahela 
shale,  sand- 
stone, lime- 
stone and  coal 


Conemaugh 

shale, 

sandstone 

and  little 

coal 


Allegheny 
shale,  sand- 
stone and  coal 


Pottsville 

sandstone 

and  some  coal 


Mauch  Chunk 

shale,  sandstone 

and  limestone 


Columnar 
section 


Thickness 
in  feet 


300+ 


310 

to 

400 


600 


280 


150 


150 


I 


> 

§  s 


Is 


PH  ' 

fl 

^4       C 

" 


§ 

•£  2 
8  M 

50  -3 


O 


THE  PENNSYLVANIAN  PERIOD  163 

system  which  is  usually  thinner  and  less  arenaceous  than  in  the 
Appalachian  district. 

Small  areas  of  Pennsylvanian  igneous  and  metamorphosed 
sedimentary  rocks,  together  with  some  graphitic  coal,  occur  in 
Rhode  Island  and  Massachusetts. 

Coal-bearing  strata  of  this  age  attain  a  thickness  of  thousands 
of  feet  in  New  Brunswick  and  Nova  Scotia. 

Pennsylvanian  Rocks  in  the  West.  —  From  the  Rocky  Moun- 
tains westward  in  the  United  States,  the  Pennsylvanian  rocks  are 
practically  all  of  true  marine  character  and  consist  largely  of 
limestone  and  sandstone  but  entirely  without  coal,  thus  being  in 
marked  contrast  with  the  rocks  of  the  system  in  eastern  North 
America. 

Thickness  of  the  Pennsylvanian.  —  In  the  Appalachian  dis- 
trict, the  system  ranges  in  thickness  from  about  1000  feet  to 
fully  7000  or  8000  feet.  A  maximum  thickness  of  13,000  feet  is 
known  in  Nova  Scotia,  and  12,000  feet  in  Rhode  Island.  Through 
the  Mississippi  Basin  the  thickness  is  usually  not  more  than  1000 
to  2000  feet,  though  in  Arkansas  a  thickness  of  over  18,000  feet 
has  been  claimed.  In  the  western  United  States  the  thickness 
varies  much,  though  it  is  usually  at  least  several  thousand  feet. 

Igneous  Rocks.  —  Considerable  amounts  of  granite  are  in- 
truded into  the  Pennsylvanian  and  other  rocks  of  Massachusetts, 
but  these  may  really  be  of  Post-Pennsylvanian  age.  Also  in  the 
Cordilleran  region  from  northern  California  to  Alaska  we  learned 
that  vulcanism  occurred  on  a  large  scale  in  Mississippian  time,  and 
it  is  probable  that  it  continued  into  Pennsylvanian  time. 

PHYSICAL  HISTORY 

Early  Pennsylvanian.  —  As  we  learned  in  the  preceding  chap- 
ter, the  Mississippian  period  closed  with  a  widespread  emergence 
of  all  (or  nearly  all)  of  the  submerged  areas  in  eastern  North 
America.  Very  early  in  the  Pennsylvanian  the  sea  began  to  trans- 
gress over  the  land  by  extending  a  long,  narrow  estuary  north- 
ward through  the  Appalachian  district  as  far  as  Pennsylvania. 
The  Pottsville  sandstones  and  conglomerates,  derived  by  erosion 
from  Appalachia  immediately  to  the  east,  were  accumulated  to 
great  thickness  in  this  estuary,  and  it  is  thus  readily  seen  why  the 
Pottsville  should  be  thickest  on  the  east  side.  Gradually  the  early 


164  HISTORICAL  GEOLOGY 

Pottsville  basin  of  deposition  expanded  and  extended  over  much  of 
the  interior  coal  fields  region.  Though  not  so  well  known,  the  best 
evidence  also  points  to  considerable  submergence  of  the  western 
United  States  in  the  early  part  of  the  period. 

Middle  and  Late  Pennsylvanian.  —  During  the  middle  Penn- 
sylvanian  the  geographic  conditions  were  essentially  as  shown  on 
the  paleogeographic  map  (Fig.  96) ,  except  that  true  marine  waters 
then  also  covered  the  temporary  land  area  in  Wyoming,  Colorado, 
and  New  Mexico.  In  the  west,  marine  conditions  prevailed  till  the 
close  of  the  period,  while  in  the  east  true  marine,  estuarine,  lacus- 
trine, marsh  or  bog,  and  possibly  even  land  conditions  alternated 
repeatedly  and  'more  or  less  locally  in  the  'basins  of  deposition. 
Since  such  remarkable  physical  geography  conditions  favored  the 
accumulation  of  the  world's  greatest  coal  beds,  they  deserve  more 
detailed  discussion.  "  Perhaps  the  most  perfect  resemblance  to 
coal-forming  condition  is  that  now  found  on  such  coastal  plains  as 
that  of  southern  Florida  and  the  Dismal  Swamp  of  Virginia  and 
North  Carolina.  Both  of  these  areas  are  very  level,  though  with 
slight  depressions  in  which  there  is  either  standing  water  or  swamp 
conditions.  In  both  regions  there  is  such  general  interference  with 
free  drainage  that  there  are  extensive  areas  of  swamp,  and  in  both 
there  are  beds  of  vegetable  accumulations.  In  each  of  these  areas 
there  is  a  general  absence  of  sediment  and  therefore  a  marked 
variety  of  vegetable  deposit.  If  either  of  these  areas  were  sub- 
merged beneath  the  sea,  the  vegetable  remains  would  be  buried 
and  a  further  step  made  toward  the  formation  of  a  coal  bed. 
Reelevation,  making  a  coastal  plain,  would  permit  the  accumula- 
tion of  another  coal  bed  above  the  first,  and  this  process  might  be 
continued  again  and  again."  1  It  is,  however,  not  necessary  to 
assume  repeated  elevation  and  subsidence  of  swamp  areas  in  order 
to  account  for  numerous  coal  beds  one  above  another  in  a  given 
region.  A  general  subsidence,  often  intermittent  (with  possibly 
some  upward  movements),  would  occasionally  cause  the  luxuriant 
vegetation  of  a  great  swamp  area  to  be  killed  and  allow  the  depo- 
sition of  sediment  over  the  site.  Then  the  filling  of  the  shallow 
water  with  sediment  would  allow  another  bog  to  be  formed,  etc. 
In  the  coal  field  of  Nova  Scotia  there  are  76  distinct  coal  beds;  in 
Alabama  35;  in  Pennsylvania  at  least  20;  and  in  Illinois  9.  Each 
of  these  coal  beds  represents  an  ancient  swamp  in  which  grew  a 
1  H.  Ries:  Economic  Geology,  1910,  p.  9. 


THE  PENNSYLVANIAN  PERIOD 


165 


PENNSYLVANIAN 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAND 
LANDS 
INDETERMINATE  AREAS 

PODAR 


CONTINENTAL  DEPOSITS,  SOMETIMES 
NCLUDING  MARINE  SEDIMENTS 
loo-  90T 


Fig.  96 

Paleogeographic  map  of  North  America  during  Pennsylvanian  time.    (Slightly 
modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.) 


166  HISTORICAL  GEOLOGY 

luxuriant  vegetation.  It  should  be  borne  in  mind  that  workable 
coal  seams  constitute  only  about  2  per  cent  of  the  containing 
strata  which  are  sandstones,  shales,  clays,  and,  in  some  localities, 
limestones. 

Perhaps  no  single  coal  seam  in  the  world  underlies  such  a  large 
area  (12,000  to  15,000  square  miles)  as  the  famous  Pittsburg  coal 
bed.  It  is  worked  over  an  area  of  about  6000  square  miles,  and  for 
2000  square  miles  it  averages  7  feet  in  thickness.  Most  of  the 
swamps  or  bogs  of  Pennsylvanian  time  were  much  smaller  than 
this. 

In  the  anthracite  coal  district  of  eastern  Pennsylvania,  the 
famous  "Mammoth"  coal  bed  is  remarkable  for  its  great  thickness 
up  to  50  or  more  feet. 

It  may  be  of  interest  to  consider  the  length  of  time  necessary 
for  the  accumulation  of  so  many  coal  beds  one  above  the  other. 
A  vigorous  growth  of  vegetable  matter  on  an  acre  has  been  esti- 
mated to  produce  the  equivalent  of  100  tons  of  dried  organic 
matter  per  century.  This  amount  con2pressed-4a^the  specific 
gravity  (1.4)  of  coal  would  cover  an  acre  less  than  two-tmrti^f  an 
inch  deep.  Considering  that  four-fifths  of  the  organic  matter 
escapes  as  gases  in  the  process  of  coal  making,  we  find  that  it  would 
take  nearly  10,000  years  to  make  one  foot  of  coal.  Now,  since  the 
total  thickness  of  coal  beds  in  the  Pennsylvanian  system  is  often 
from  100  to  250  feet,  it  is  readily  seen,  on  this  basis,  that  the  time 
necessary  for  the  accumulation  of  the  coal  deposits  was  from 
1,000,000  to  2,500,000  years.  On  a  conservative  basis,  the  time 
necessary  for  the  deposition  of  the  sediments  was  fully  as  long, 
so  that  the  Pennsylvanian  period  appears  to  have  had  a  duration  of 
no  less  than  2,000,000  to  5,000,000  years. 

Close  of  the  Pennsylvanian.  —  At  the  end  of  the  period  the 
remarkable,  near  sea-level,  coal-swamp  geographic  conditions  in 
the  eastern  United  States  were  largely  brought  to  a  close  by  emer- 
gence of  the  lands  distinctly  above  sea  level,  except  in  a  narrow 
trough  lying  along  the  western  side  of  the  Appalachian  Moun- 
tain axis  and  in  which  Permian  deposits  accumulated.  From  the 
Great  Plains  westward  also  the  marine  waters  were  notably  re- 
stricted. In  the  east,  at  least,  the  emergence  was  probably  due  to 
a  beginning  of  the  great  orogenic  movements  which  culminated 
in  the  Appalachian  Mountain  Revolution  at  the  close  of  the 
Paleozoic  era. 


THE  PENNSYLVANIAN  PERIOD 


167 


FOREIGN  PENNSYLVANIAN 

Europe.  —  Viewed  in  a  broad  way,  the  Pennsylvanian  of 
Europe  presents  certain  interesting  parallels  with  North  America. 
Thus  in  Europe,  sandstone  or  conglomerate,  corresponding  to  our 
Pottsville,  often  lies  at  the  base  of  the  system.  Above  this,  in 


Fig.  97 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  during 
Pennsylvanian  (Upper  Carboniferous)  time.  Finer  dotted  areas 
were  covered  by  marine  water,  and  coarser  dotted  areas  repre- 
sent lagoons  or  basins  of  continental  deposition.  (Slightly  modified 
after  De  Lapparent.) 

western  Europe,  are  the  Coal  Measures  consisting  of  shales,  sand- 
stones, and  some  limestones  together  with  numerous  beds  of  coal, 
and  in  every  way  much  like  the  Coal  Measures  of  eastern  North 
America  (Fig.  95).  In  western  and  southern  Europe  the  rocks  are 
largely  true  marine  limestones  and  free  from  coal,  though  some 
coal  does  exist  in  southern  Russia. 

Igneous  rocks  were  intruded  into  the  strata  of  western  Europe 


168  HISTORICAL  GEOLOGY 

during  the  Pennsylvania!!,  the  vulcanism  probably  being  a  con- 
tinuation of  that  begun  in  the  preceding  period. 

Other  Continents.  —  Much  rock  of  Pennsylvanian  age,  both 
of  marine  and  non-marine  origin,  occurs  in  Asia,  with  coal  beds 
in  Asia  Minor,  the  east  side  of  the  Ural  Mountains,  and  in  northern 
China.  The  coal  beds  of  China  are  said  to  be  extensive  and 
important. 

Marine  strata  without  coal  occur  in  northern  Africa.  In  the 
Zambesi  district  of  southern  Africa  a  coal  field  is  known. 

In  Australia  and  South  America  marine  and  non-marine  strata 
of  this  age  are  also  pretty  widespread.  Much  coal  occurs  in 
southern  Brazil. 

CLIMATE 

Until  comparatively  recently  the  plant  life  of  the  great  coal 
period  was  thought  to  imply  a  warm  to  tropical,  very  moist, 
uniform  climate.  More  careful  study,  however,  clearly  points  to 
a  temperate,  only  relatively  humid,  but  remarkably  uniform 
climate.  Some  of  the  criteria  favoring  this  latter  view  may  be 
stated  as  follows : x  The  great  size  and  height  of  the  plants 
together  with  their  frequent  succulent  nature  and  spongy  leaves 
indicate  luxuriant  growth  in  a  moist,  mild  climate;  absence  of 
annual  rings  of  growth  shows  absence  of  distinct  change  of  seasons; 
the  presence  of  aerial  roots,  by  analogy  with  similar  modern  plants, 
implies  a  moist  and  warm  climate;  the  nearest  present-day  allies 
of  the  coal  plants  attain  greatest  growth  in  warm  and  humid 
climates;  at  present  the  greatest  accumulations  of  vegetable 
matter  in  bogs  and  marshes  take  place  in  temperate  climates 
where  decay  is  not  too  rapid  and  thus  suggests  a  similar  climate 
for  the  accumulation  of  the  coal  deposits;  and  the  remarkable 
distribution  of  almost  identical  plant  types  in  Pennsylvanian 
rocks  from  Arctic  to  tropical  regions  clearly  shows  a  pronounced 
uniformity  of  climate  over  the  earth. 

ECONOMIC  PRODUCTS 

As  already  suggested,  the  principal  economic  product  of  Penn- 
sylvanian age  is  coal,  the  richest  and  most  extensive  coal  deposits 
in  the  world  being  of  this  age.  Eastern  North  America,  western 

1  Based  upon  the  work  of  D.  White:  Jour.  GeoL,  Vol.  17,  1909,  p.  338. 


THE  PENNSYLVANIAN  PERIOD  169 

Europe,  and  northern  China  contain  the  most  important  coal 
fields.  The  map  (Fig.  93)  gives  a  general  idea  of  the  locations  of 
the  coal  fields  of  eastern  North  America,  though  several  of  the 
areas  of  coal-bearing  Pennsylvanian  rocks  are  really  somewhat 
larger  than  this  surface  distribution  (or  outcrop)  map  shows. 
These  areas,  largely  underlain  with  workable  coal,  are  as  follows: 

(1)  Anthracite  field  of  eastern  Pennsylvania  —  484  square  miles; 

(2)  Appalachian  field  from  western  Pennsylvania  to  Alabama  — 
70,000  square  miles;   (3)  Eastern  Interior  field  in  Indiana,  Illi- 
nois,  and  Kentucky  —  50,000  square  miles;     (4)  Northern  In- 
terior field    in   Michigan — 11,000   square   miles;    (5)    Western 
Interior  field  from    Iowa  to  Oklahoma  —  72,000  square  miles; 
(6)    Texas  field— 13,000   square   miles;   and   (7)   Nova  Scotia- 
New  Brunswick  field  — 18,000  square  miles.     Thus  in  eastern 
North  America  a  total  of  about  235,000  square  miles  is  mostly 
underlain  with  workable  coal  of  Pennsylvanian  age.     Consider- 
able coal  of  this  age  also  occurs  in  Alaska. 

Iron  ores  of  some  importance  are  found  in  the  carbonate  and 
oxide  forms  as  bedded  deposits  in  Pennsylvanian  rocks.  Such 
deposits  were  formed  by  precipitation,  in  the  marshes  and  swamps, 
of  the  iron  brought  down  from  the  lands  in  soluble  form.  The 
principal  deposits  occur  in  western  Pennsylvania,  eastern  Ohio, 
and  northern  West  Virginia. 

Pennsylvanian  rocks  also  yield  considerable  oil  and  gas  espe- 
cially in  Illinois,  Kansas,  and  Oklahoma. 

LIFE  OF  THE  PENNSYLVANIAN 

IN  all  of  the  preceding  periods,  our  studies  of  organisms 
have  been  chiefly  confined  to  marine  forms  because  either 
they  only  existed,  or  predominated,  or  because  they  have  left 
us  the  most  abundant  records.  Rocks  of  the  Pennsylvanian  sys- 
tem are  the  earliest  to  carry  abundant  records  of  land  plants 
and  animals  (Amphibians),  and  for  the  first  time  our  principal 
discussion  of  the  life  of  a  period  will  deal  with  such  forms.  The 
Coal  Measures  and  their  enclosed  organic  remains  have  been 
studied  in  unusual  detail  because  of  the  economic  value  of  the  coal. 

Plants.  —  The  plant  life  of  Pennsylvanian  time  was  very 
prolific  and  the  records  for  this  period  are  far  more  abundant  than 
for  any  other  Paleozoic  period,  one  reason  for  this  unusually  full 


170 


HISTORICAL  GEOLOGY 


record  doubtless  being  the  very  favorable  conditions  for  pres- 
ervation of  the  flora  of  the  time.  Several  thousand  species  of  now 
extinct  plants  are  known  from  the  Coal  Measures  alone.  It  must 
be  remembered  that  most  of  the  important  classes  of  Pennsylva- 
nian  plants  existed  as  early  as  in  the  Devonian,  but  these  earlier 
records  are  much  more  scant.  The  known  Coal  Measures  flora 
consists  almost  entirely  of  the  higher  Cryptogams  (Pteridophytes) 
and  the  lower  Phanerogams  (Gymnosperms) ,  though  Thallophytes 
(e.g.  Alga3)  certainly,  and  Bryophytes  probably,  also  existed. 

From  the  negative  standpoint, 
the  most  significant  feature  was 
the  complete  absence  of  the 
typical  flowering  plants  (Angio- 
sperms)  which  are  today  the 
most  common  and  the  most 
advanced  of  all  plants. 

Lycopods  (giant  Club-mos- 
ses) were  the  largest,  most 
abundant,  and  conspicuous  of 
the  forest  trees,  and  they  ap- 
pear to  have  culminated  during 
this  same  period.  In  marked 
contrast  to  such  a  high  posi- 
tion, their  descendants  of  today 

are  represented  only  by  a  few,  small,  delicate,  trailing  so-called 
Club-mosses  and  Ground-pines  in  our  forests.  Two  of  the  most 
prominent  of  the  Pennsylvanian  Lycopods  were  the  Lepidodendrons 
and  the  Sigillarians.  The  Lepidodendrons  (" scale-trees")  had  leaf- 
scars  or  scales  arranged  spirally  around  the  trunks  of  the  trees  (Fig. 
98a).  They  generally  attained  a  height  of  50  to  100  feet  and  a  di- 
ameter of  2  to  4  feet.  The  tall  trunks  were  slender  and  they 
branched  dichotomously  (by  twos)  only  at  a  considerable  height. 
Long,  stiff,  needle-shaped  leaves  were  thickly  set  on  the  branches. 
The  dropping  of  the  leaves  from  the  older  (trunk)  portions  caused 
the  leaf-scars  or  scales  above  mentioned.  Inside  of  the  outer  bark, 
the  stem  consisted  of  pithy  or  loose  cellular  tissue.  Over  100 
species  of  the  Lepidodendron  are  known.  The  Sigillarians  ("  seal- 
trees")  are  so  called  because  of  seal-like  markings  (Fig.  98b) 
which  were  arranged  vertically  on  the  tree  trunk.  They  were  even 
larger  than  the  Lepidodendrons,  having  attained  a  height  of  100 


a  b 

Fig.  98 

Lepidodendron  bark  (a)  and  Sigillarian 
bark  (6),  showing  arrangement  of 
leaf  scars. 


THE  PENNSYLVANIAN  PERIOD 


171 


feet  or  more  and  a  diameter  of  5  or  6  feet.  The  trunk  seldom 
branched  and  it  ended  with  a  rounded  tip.  In  other  respects  these 
trees  were  much  like  the  Lepidodendrons. 

Equisetce  (" Horse-tail"  plants)  were  also  common  in  the  Penn- 
sylvanian  forests.  These  plants  had  long,  slender,  segmented 
stems  which  were  either  hollow  or  filled  with  a  large,  soft  pith 


Fig.  99 

Fronds  of  a  Pennsylvania!!  Fern,  Mariopteris.     (After  D.  White,  U.  S.  Geo- 
logical Survey,  Monograph  37.) 

(Fig.  101).  The  leaves,  which  were  arranged  in  whorls  around  the 
stems  at  the  joints,  were  of  variable  shapes  and  sizes,  usually  either 
needle-like,  scale-like,  or  strap-like.  The  outside  of  the  stem  had  a 
sort  of  finely  fluted  structure  but  without  scars  and  not  continuous 
as  in  the  Sigillarians.  They  reached  heights  of  60  to  90  feet  and 
diameters  of  1  or  2  feet.  Equisetse  are  today  chiefly  represented 
by  only  a  few  species  of  rush-like  forms  not  over  a  few  feet  high, 
though  in  South  America  some  very  slender  forms  grow  to  heights 
of  30  or  40  feet. 


172 


HISTORICAL  GEOLOGY 


Filices  (true  Ferns)  were  very  abundant  and  diversified,  both 
as  tree-like  forms  and  as  small,  herbaceous  forms.  Both  forms 
were  very  similar  in  appearance  to  those  now  living  in  tropical 
and  temperate  climates  (Figs.  99-100). 

Cycadofilices  (" Seed-ferns"),  which  were  common  in  the  Penn- 
sylvanian,  comprise  a  remarkable  group  of  plants  recently  regarded 
as  transitional  between  the  Cryptogams  and  Phanerogams.  They 
possessed  seeds  but  not  flowers  and  showed  many  features  which 
seem  to  make  them  the  connecting  link  between  the  Filices  and  the 

Cycads,  hence  the  name  "  Cycadofili- 
ces." The  seeds  were  arranged  on 
the  leaves.  There  is  considerable  dif- 
ference of  opinion  concerning  the 
relations  and  affinities  of  this  remark- 
able group  of  plants,  now  long  extinct 
(Fig.  102). 

Gymnosperms. — Of  these  the  most 
abundant  representatives  were  the 
Cordaites.  They  were  comparatively 
slender  trees  which  attained  a  diam- 
eter of  2  or  3  feet  and  a  height  of  90 
feet  or  more  (see  Fig.  103).  The 
branches,  which  were  given  off  only 
toward  the  top  of  the  trunk,  were 
supplied  with  numerous,  long,  very 
simple,  parallel-veined,  strap-shaped 
leaves  notable  for  great  size,  some- 
times 5  or  6  feet  long  and  5  or  6  inches  wide.  The  trunks  were 
covered  with  thick  bark,  while  inside  there  was  much  pith.  Many 
specimens  have  been  well  preserved.  They  were  important  contrib- 
utors to  the  formation  of  some  coal  beds.  They  possessed  certain 
features  or  structures  of  the  Seed-ferns,  Conifers,  Cycads,  and  Gink- 
gos  in  addition  to  their  own  characteristics.  Cordaites  thus  afford 
a  fine  illustration  of  a  generalized  type  of  plant,  that  is  to  say  one 
which  combined  the  characters  of  several  distinct  (some  later)  forms. 
True  Cycads  and  Conifers  are  not  certainly  known  to  have 
existed  in  the  Pennsylvanian  period,  though  some  paleobotanists 
claim  their  existence. 

Protozoans.  —  Foraminifers  were  very  abundant  as  proved  by 
the  vast  numbers  of  tiny  wheat-like  shells  which  contributed  much 


Fig.  100 

A  Living  Tree-fern.  (From 
Le  Conte's  "Geology,"  per- 
mission of  D.  Appleton  and 
Company.) 


THE  PENNSYLVANIAN  PERIOD 


173 


to  building  up  certain  Pennsylvanian  limestones  in  America, 
Europe,  and  other  continents. 

Porifers.  —  Sponges  were  present  but  they  require  no  special 
mention. 

Coelenterates.  —  Among  these  the  Corals  only  have  left 
records,  and  even  these  do  not  appear  to  have  been  abundant.  In 


Fig.  101 

A  Permo-Carboniferous  landscape,  showing  some  of  the  most  conspicuous 
plants  of  the  great  Coal  Age.  Lepidodendrons  (with  branches)  and  Sigil- 
larians  (without  branches)  in  the  left  background;  Equisetae  (segmented) 
on  the  right;  Seed-ferns  in  the  left  foreground;  two  Amphibians  (Eryops) 
on  the  land;  a  primitive  Reptile  (Limnoscelis)  in  the  water;  and  a  great 
Insect  (Dragon-fly)  in  the  air.  (From  a  drawing  by  Prof.  S.  W.  Williston.) 


eastern  North  America  and  western  Europe  the  physical  geography 
conditions  were  distinctly  unfavorable  to  them. 

Echinoderms.  —  Of  the  Pelmatozoans  (stemmed  Echinoderms) 
only  the  Blastoids  and  Crinoids  remained,  the  former  having 
become  extinct  during  the  period.  The  Crinoids  showed  a  remark- 


174  HISTORICAL  GEOLOGY 

able  falling  off  after  their  culmination  in  the  Mississippian,  but 
in  the  Mesozoic  they  regained  prominence. 

Asterozoans  of  this  age  have  not  been  found  in  fossil  form, 
but,  judging  by  their  previous  and  subsequent  history,  they  must 
have  existed. 

Echinoids  were  much  like  the  Mississippian  forms  though  rare. 


Fig.  102 

A  Cycadofilices  or  Seed-fern.  Restored  by  D.  H.  Scott  and  J.  Allen.  (From 
Chamberlin  and  Salisbury's  "Geology,"  courtesy  of  Henry  Holt  and 
Company.) 

Molluscoids.  —  Bryozoans  continued  to  be  common,  though 
the  peculiar  spiral  forms  (Archimedes)  disappeared. 

Brachiopods  were  still  common  but  by  no  means  as  prominent 
as  in  earlier  Paleozoic  periods.  They  were  much  like  the  Missis- 
sippian forms.  A  noteworthy  fact  was  the  almost  world-wide 
distribution  of  some  of  the  species,  which  indicates  either  actual 
land  bridges  or  at  least  shallow  water  areas  connecting  all  the 
continents. 


THE  PENNSYLVANIAN  PERIOD  175 

Mollusks.  —  Pelecypods  showed  advancement  in  numbers  and 
species  and  closer  approach  to  modern  species  in  appearance. 

Gastropods  continued 
to  be  much  like  those  of 
earlier  periods.  It  is  im- 
portant to  note  that  sev- 
eral species  of  the  earliest 
known  land  (air-breathing) 
Gastropods  (Snails)  have 
been  found. 


Fig.  104 

A  Pennsylvanian  Go- 
niatite.  (Goniatites 
lyoni.  After  Meek.) 

Cephalopoda,  both 
Nautiloids  and  Ammonoids 
were  much  as  in  the  Mis- 
sissippian,  though  the 
former  had  somewhat  di- 
minished and  the  latter 
showed  gradually  increas-  Fl&-  103 

ing  complexity  of   suture     Cordaites    restored.      (From    Schuchert's 
/tx       •tf\A\  'Historical  Geology,     courtesy  ot  John 

structure  (Fig.  104).  Wifey  and  gons  }  ^ 

Arthropods.  —  Trilo- 

bites  were  few  and  unimportant  and  close  to  the  period  of  their 
extinction. 

Eucrustaceans  of   Shrimp-like   and   Crayfish-like   forms  were 
present  but  not  common  (Fig.  105). 

Arachnids  were  well  represented  by  both  Spiders  and  Scorpions, 


176 


HISTORICAL  GEOLOGY 


a  b 

Fig.  105 

Pennsylvania!!  Eucrustaceans :  a,  Anthrapalcemon  gracilis  (Meek 
and  Worthen);  b,  Euproops  dance  (Meek  and  Worthen).  (From  Le 
Conte's  "Geology,"  permission  of  D.  Appleton  and  Company.) 

the  former  having  made  their  first  known  appearance.    They  looked 
much  like  existing  forms  (Fig.  106).     Eurypterids  still  continued 


a  b 

Fig.  106 

Pennsylvanian  Arachnids:  a,  Scorpion,  Eoscorpius  carbonarius  (Meek 
and  Worthen);  6,  Spider,  Anthrolycosa  antiqua  (Beecher).  (From  Le 
Conte's  "Geology,"  permission  of  D.  Appleton  and  Company.) 


THE  PENNSYLVANIAN  PERIOD  177 

though  not  in  abundance.  Their  common  associations  with  land 
and  fresh-water  plants  and  animals  clearly  proves  many  at  least 
to  have  been  fresh-water  dwellers. 

Myriapods  were  plentiful. 

Insects.  — A.S  would  be  expected  in  accordance  with  the 
abundant  and  favorable  plant  environment,  the  Insects  showed 
a  notable  development.  Hundreds  of  species  are  known  from 
the  Coal  Measures  of  America  alone.  Nearly  all  were  of  simple 
types  belonging  to  the  Orthopters  and  Neuropters,  which  orders 


Fig.  107 

A  Pennsylvanian  Insect,  Corydaloides  scudderi  (Brongniart) . 
This  Insect  had  a  spread  of  wing  of  18  inches.  (From  Le 
Conte's  "Geology,"  permission  of  D.  Appleton  and  Company.) 

are  represented  by  modern  Grasshoppers,  Cockroaches,  Caddis- 
flies,  etc.  Somewhat  higher  types  may  possibly  have  been  present, 
but  the  highest  Insects,  such  as  Butterflies,  Bees,  Ants,  etc.,  are 
not  known  to  have  existed.  Two  other  noteworthy  facts  regarding 
Pennsylvanian  Insects  are:  (1)  Their  great  size,  some  having  had 
a  spread  of  wing  of  from  1  to  2J  feet  (Fig.  107) ;  and  (2)  the  exist- 
ence of  three  pairs  of  wings  on  some  species. 

Vertebrates.  —  Fishes  continued  much  the  same  as  in  the 
Mississippian  and  they  require  no  special  mention  here. 

Amphibians  for  the  first  time  left  abundant  records  in  the 
Pennsylvanian  rocks,  and  they  merit  special  discussion  here.  This 
was  probably  the  culminating  period  of  the  Amphibians,  and  from 


178 


HISTORICAL  GEOLOGY 


the  standpoint  of  the  evolution  of  the  air-breathing  Vertebrates 
the  Pennsylvanian  is  regarded  as  the  most  important  period  in  geo- 
logical history.  It  is  to  be  remembered  that  the  earliest  Amphib- 
ians almost  certainly  evolved  from  certain  types  of  Fishes.  All 
Mississippian  and  Pennsylvanian  Amphibians  are  often  classed 
together  as  Stegocephalians,  so-called  because  of  the  relatively 
large,  bony,  roof-like  plates  of  the  skulls. 

As  regards  the  principal  forms  of  Amphibians  of  Pennsylvanian 
time,  the  writer  can  do  no  better  than  to  quote  an  excellent  sum- 


Fig.  108 

A  Pennsylvanian  Amphibian  (Labyrinthodont),  Eryops.  This  creature  at- 
tained a  length  of  6  or  8  feet.  (Courtesy  of  the  American  Museum  of 
Natural  History.) 

mary  by  S.  W.  Williston:1  "The  predominating  types  of  the 
Pennsylvanian  were  what  we  usually  call  the  Branchiosaurs  and 
the  Microsaurs,  for  the  most  part  small  or  very  small  creatures,  at 
least  as  small  as  their  nearest  living  relatives  of  the  present  time, 
the  Salamanders.  We  are  quite  justified  in  the  belief  that  their 
habits  in  general  were  not  greatly  unlike  these  descendants,  rather 
sluggish  creatures  living  about  or  in  the  water,  for  the  Branchio- 
saurs at  least  passed  through  larval  stages.  They  were  more  or 
less  protected  by  an  external  bodily  armor  against  their  enemies, 
whether  of  their  own  or  other  kinds,  in  all  probability  terminat- 
ing their  existence  as  distinctive  types  long  before  the  close  of 
the  Paleozoic.  But  among  them  there  were  some  classed  with  the 

1  Outlines  of  Geologic  History,  1910,  p.  164. 


THE   PENNSYLVANIAN  PERIOD 


179 


heterogeneous  group  which  we  call  Microsaurs,  which  had  made 
a  very  distinct  advance,  both  toward  a  higher  existence  and  away 
from  the  water.  .  .  .  Some  lost  the  dermal  armor  completely 
and  became  fleet  of  movement,  as  is  evidenced  by  the  structure 
of  the  limbs,  limbs  mimicking  in  form  and  structure  so  closely 
those  of  modern  quick-run- 
ning Lizards  as  to  be  prac- 
tically indistinguishable." 

The  Labyrinthodonts, 
and  certain  other  closely 
related  forms,  comprised 
another  important  group 
of  Pennsylvanian  Amphib- 
ians. They  are  so  named 
because  of  the  peculiar, 
labyrinthine,  internal 
tooth-structure  (Fig.  109). 
They  were  the  gigantic 
land  Vertebrates  of  the 
period,  some  having 
reached  a  length  of  7  or  8 
feet  (Fig.  108). 

Reptiles.  —  Whether  or  not  true  Reptiles  existed  in  this  period 
depends  largely  upon  the  classification  of  the  primitive  land  Ver- 
tebrates. The  abundance  of  true  Reptiles  in  the  succeeding  (Per- 
mian) period  strongly  suggests  their  earlier  differentiation  from 
the  Amphibians.  According  to  Williston:  "We  may  be  assured 
that  some  of  them  (Amphibians) ,  before  the  close  of  the  Pennsyl- 
vanian, were  inhabitants  of  high-and-dry  land  regions  where  fleet- 
ness  of  movement,  rather  than  obscurity,  preserved  them  from  their 
enemies,  crawling  Reptiles  in  everything  save  some  insignificant 
technical  details  of  their  plates." 


Fig.  109 

Transverse  section  of  a  Labyrinthodont 
tooth.  (After  Owen  from  Norton's 
"Elements  of  Geology,"  by  permission 
of  Ginn  and  Company,  Publishers.) 


CHAPTER  XII 


THE    PERMIAN    PERIOD 
ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

THIS  period  was  so  named  by  Murchison  in  1841  because  of 
the  widespread  development  of  rocks  of  this  age  in  the  Russian 
province  of  Perm.  It  is  pretty  distinctly  a  transition  period  be- 
tween the  Paleozoic  and  Mesozoic  eras.  In  both  the  eastern  and 
western  United  States  the  Pennsylvanian  rocks  usually  grade 
upward  into  the  Permian,  while  in  the  western  regions  the  Permian 
strata  nearly  always  grade  upward  into  the  Triassic.  Thus  it  is 
well-nigh  impossible  to  sharply  separate  the  Permian  from  the 
systems  immediately  above  and  below  it,  and  the  delimitation  of 
the  Permian  system  in  western  America  is  by  no  means  a  settled 
matter  at  the  present  time.  The  scarcity  or  absence  of  fossils  in 
many  of  the  western  areas  adds  to  the  difficulty. 

The  following  table  will  give  a  general  idea  of  the  subdivisions 
now  recognized  in  some  of  the  better  known  regions,  though  it  must 
be  clearly  understood  that  precise  correlations  are  not  meant  to 
be  implied. 


Texas 

.Kansas 

Pennsylvania 

Double  Mountain  series 

Cimarron  (Red  Beds)  series 

(Salt,     gypsum,    and 

(Sandstones,  shales,  dolo- 

limestone). 

mites,  and  gypsum). 

PERMIAN 
SYSTEM 

Clear  Fork  series 
(Limestone    and   red 
clay)  . 

Dunkard 
series 
(Sandstones, 

Wichita  series 

Big  Blue  series 

shales,  lime- 

(Red clay,  sandstone, 

(Shales  and  limestones). 

stones,    and 

and  limestone). 

some  coal.) 

180 


THE  PERMIAN  PERIOD  181 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  Compared  with  the  preceding  Pal- 
eozoic systems,  the  Permian  rocks  have  a  rather  limited  distribu- 
tion. There  are  small  areas  in  Nova  Scotia  and  New  Brunswick; 
a  small  area  in  Pennsylvania,  Ohio,  and  West  Virginia;  large  areas 
in  Texas,  Oklahoma,  Kansas,  Colorado,  Nebraska,  and  Iowa; 
smaller  areas  in  South  Dakota  and  Wyoming;  and  some  rather 
poorly  known  areas  in  New  Mexico,  Utah,  northern  Arizona, 
northern  California,  and  the  Pacific  border  of  Alaska.  All  of  these 
surface  exposures  are  within  the  areas  represented  on  the  map 
(Fig.  Ill)  either  as  occupied  by  marine  waters  or  receiving  con- 
tinental deposits. 

In  the  western  United  States  the  Permian  strata  are  consider- 
ably more  extensive  than  their  surface  distribution  because  they 
are  concealed  under  Mesozoic  or  Cenozoic  rocks  over  large  areas. 
Also  there  is  some  reason  to  think  that  the  Permian  strata  for- 
merly extended  over  much  of  the  Great  Basin  region,  but  have 
been  removed  by  erosion,  leaving  much  Pennsylvanian  or  Missis- 
sippian  rock  now  at  the  surface.  In  the  eastern  United  States, 
however,  the  one  small  area  in  the  northern  Appalachian  district 
comprises  all  of  the  Permian  except  possibly  some  in  the  lower 
Mississippi  Valley  where  Mesozoic  and  later  rocks  effectually  con- 
ceal the  older  rocks. 

Character  of  the  Rocks.  —  The  Permian  strata  (Dunkard 
series)  in  the  small  area  of  the  northern  Appalachian  district  are 
sandstones  and  shales,  together  with  some  limestone  and  coal  beds. 
They  are  in  every  way  much  like  the  Coal  Measures  just  below. 

In  Kansas  the  Permian  rocks  are  divisible  into  two  rather  dis- 
tinct series,  the  lower  or  Big  Blue  series  of  shales  and  limestones 
being  largely  marine,  while  the  upper  or  Cimarron  series  of  sand- 
stones, shales,  dolomitic  limestones,  and  gypsum  are  mostly  not 
truly  marine  and  they  are  characterized  by  a  prevailing  red  color. 

The  Texas  Permian  strata  are  chiefly  red  beds  of  mostly  non- 
marine  origin  and  divisible  into  three  series  as  shown  above.  Red 
clays,  limestones,  and  sandstones  constitute  the  two  lower  series, 
while  limestone,  salt,  and  gypsum  chiefly  make  up  the  upper  series. 

Marine  Permian  strata  of  considerable  thickness  have  been 
reported  from  the  Wasatch  Mountains  of  Utah,  and  from  northern 
California. 


182 


HISTORICAL  GEOLOGY 


Strata,  mostly  of  non-marine  origin  and  containing  much  red 
materials  like  those  of  Texas  and  Kansas,  are  also  found  in  the 
other  western  states  where  Permian  rocks  occur  (see  above,  also 
Fig.  110). 

True  marine  strata,  some  thousands  of  feet  thick,  are  known  in 
Alaska,  especially  in  the  Copper  River  region. 

In  Nova  Scotia  and  New  Brunswick  the  Permian  also  consists 
mostly  of  red  beds  including  conglomerates,  sandstones,  and  shales. 


'  -    k:% 


Fig.  110 

Late  Permian  or  early  Triassic  "Red  Beds"  in  Red  Butte,  eastern  Wyoming. 
The  bright  red  strata  are  capped  by  a  30-foot  layer  of  white  gypsum.  (After 
Barton,  U.  S.  Geological  Survey,  Folio  127.) 

Thickness  of  the  Permian.  —  In  Pennsylvania  and  Ohio  the 
Dunkard  series  (Lower  Permian  only)  shows  a  thickness  of  about 
1000  feet.  A  thickness  of  2000  feet  for  the  whole  system  is  re- 
ported from  Kansas;  5000  to  7000  feet  in  Texas;  and  3800  feet 
in  Utah.  In  Nova  Scotia  and  New  Brunswick  Permian  strata 
attain  a  maximum  thickness  of  8000  feet. 

Igneous  Rocks.  —  Evidence  of  vulcanism  during  the  Permian 
period  in  North  America  is  practically  absent. 


THE  PERMIAN  PERIOD  183 


PHYSICAL  HISTORY 

During  the  Period.  —  Combining  the  above  descriptions  of 
rock  distribution  and  characters  with  an  examination  of  the 
paleogeographic  map,  the  physical  history  of  North  America 
during  the  Permian  may  be  readily  comprehended.  True  marine 
conditions  are  definitely  known  to  have  prevailed  during  the  whole 
period  only  in  southern  Alaska,  northern  California,  Utah,  and 
possibly  southern  New  Mexico.  The  visible  Permian  strata  in 
most  of  the  other  western  states  are  of  such  character  as  to  indicate 
deposition  in  great  salt  lakes  or  more  or  less  cut  off  basins  or  arms 
of  the  sea.  Conditions  of  aridity  must  have  prevailed.  Inter- 
bedded  with  these  deposits,  however,  in  some  areas  are  marine 
strata,  thus  proving  at  least  occasional  incursions  of  the  sea.  In 
Kansas  the  character  of  the  rocks  shows  the  prevalence  of  marine 
waters  during  much  of  the  earlier  Permian.  The  best  evidence 
seems  to  indicate  that  these  interior  basins  had  their  connections 
with  the  sea  across  the  Great  Basin  region  (as  indicated  by  true 
marine  strata  in  the  Wasatch  Mountains)  on  one  side,  and  through 
southern  New  Mexico  and  northern  Mexico  on  the  other,  with  an 
island  between  as  shown  on  the  map  (Fig.  111). 

The  rocks  of  the  northern  Appalachian  district  clearly  prove 
a  continuation  of  the  Coal  Measures  conditions,  that  is  great 
fresh-water  lagoons  or  basins,  with  occasional  sea  incursions. 

The  Nova  Scotia  and  New  Brunswick  Permian  rocks  are  also 
chiefly  of  continental  origin,  suggesting  conditions  of  deposition 
similar  to  those  in  the  western  states,  except  that  salt  and  gypsum 
are  practically  absent. 

Close  of  the  Permian  (Appalachian  Revolution)  — The 
Paleozoic  era  was  brought  to  a  close  by  one  of  the  most  profound 
physical  disturbances  in  the  history  of  North  America.  It  has 
been  called  the  Appalachian  Revolution  because  at  that  time  the 
Appalachian  Mountain  Range  was  born  out  of  the  sea  by  upheaval 
and  folding  of  the  strata.  Perhaps  it  would  be  better  to  say  that 
the  revolution  reached  its  climax  at  about  the  close  of  the  Paleozoic 
because  the  evidence  is  clear  that  the  upward  movement  began  at 
least  as  early  as  the  close  of  the  Mississippian  and  slowly  increased 
to  the  close  of  the  era.  Since  Permian  strata  are  involved  in 
the  folding  along  the  western  side  of  the  Appalachians,  we  know 


184 


HISTORICAL  GEOLOGY 


LATEST  PALEOZOIC 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  WORE  LIKELY  LAKD 
LANDS 
INDETERMINATE  AREAS 

POLAR 


CONTINENTAL  DEPOSITS.  SOMETIMES 
INCLUDING  MAR1KH  SEDIMENTS 


Fig.  Ill 

Paleogeographic  map  of  North  America  during  latest  Paleozoic  (Permian) 
time.  Outcrops  of  Permian  strata  are  confined  to  the  vertical  and  oblique- 
lines  areas,  and  in  this  way  the  map  may  also  be  regarded  as  a  Permian 
surface  distribution  map.  (Slightly  modified  after  Bailey  Willis,  courtesy 
of  The  Journal  of  Geology.} 


THE  PERMIAN  PERIOD  185 

that  much  of  the  disturbance  must  have  occurred  after  the  deposi- 
tion of  those  strata. 

All  through  the  vast  time  (at  least  10,000,000  years)  of  the 
Paleozoic  era,  a  great  land-mass  (Appalachia)  existed  along  what 
is  now  the  eastern  coast  of  the  United  States.  Its  western  boundary 
was,  most  of  the  time,  just  east  of  the  present  Appalachians,  while 
it  must  have  ext&hded  eastward  at  least  as  far  as  the  border  of  the 
continental  shelf.  ^Concerning  the  altitude  and  the  character  of 
the  topography  of  Appalachia  we  know  almost  nothing,  but  we 
do  know  that  it  consisted  of  rock  of  pre-Cambrian  age.  The  enor- 
mous amount  of  sediment  derived  from  it  shows  that  Appalachia 
was  high  enough  during  nearly  all  of  its  history  to  undergo  vigorous 
erosion.  Although  oscillations  of  level  more  than  likely  affected 
the  land-mass,  and  its  western  shore  line  was  quite  certainly 
shifted  at  various  times,  nevertheless  it  persisted  as  a  great  land 
area  with  approximately  the  same  position  during  all  of  its  long 
history.  Its  general  position  is  well  shown  on  the  various  Paleozoic 
paleogeographic  maps. 

Barring  certain  minor  oscillations  of  level,  all  of  the  region  just 
west  of  Appalachia  was  occupied  by  sea  water  during  the  whole  Pal- 
eozoic era,  and  sediments  derived  from  the  erosion  of  Appalachia 
were  laid  down  layer  upon  layer  upon  that  sea  bottom.  The 
coarsest  and  greatest  thickness  of  sediments  deposited  nearest 
the  land,  that  is  along  what  we  might  call  the  marginal  sea  bottom. 
At  the  same  time,  finer  sediments  and  limestones  in  thinner  sheets 
were  being  deposited  over  much  of  the  Mississippi  Valley  region. 
By  actual  measurement,  in  the  present  Appalachians,  we  know 
that  the  maximum  thickness  of  these  sediments  was  at  least 
25,000  feet.  Now,  since  these  are  all  of  comparatively  shallow 
water  origin,  as  proved  by  the  coarseness  of  sediments,  ripple- 
marks,  fossil  Coral  reefs,  etc.,  we  are  forced  to  conclude  that  this 
marginal  sea  bottom  gradually  sank  during  the  process  of  sed- 
imentation, thus  producing  what  is  called  a  great  geosynclinal 
trough.  Perhaps  the  very  weight  of  accumulating  sediments 
caused  this  sinking.  Finally,  toward  the  close  of  the  Paleozoic  era, 
sinking  of  the  marginal  sea  bottom  and  deposition  of  sediments 
ceased,  and  a  tremendous  force  of  lateral  compression  was  brought 
to  bear,  causing  the  strata  to  become  folded  and  more  or  less  frac- 
tured. Thus  arose  the  great  Appalachian  Mountain  range  which,  in 
its  prime,  was  doubtless  much  loftier  than  it  is  today  (see  Fig.  112). 


186 


HISTORICAL  GEOLOGY 


This  tremendous  deformation  took  place  very  slowly,  though 
during  a  short  time  as  compared  with  the  length  of  the  Paleozoic 
era.  As  soon  as  the  folds  appeared  well  above  sea-level,  irregu- 


Fig.  112 

Highly  generalized  structure  sections  across  the  Appala- 
chian Mountains  and  adjoining  districts  to  illustrate 
certain  important  features  in  the  history  of  the  region. 

Upper  figure:  A,  Appalachia;  B,  marginal  sea-bottom 
(Appalachian  geosyncline)  mostly  filled  with  sediments 
derived  from  Appalachia  during  Paleozoic  time. 

Middle  figure:  The  same  region  with  the  strata  folded 
into  mountains  as  they  would  have  appeared,  if  un- 
affected by  erosion,  toward  the  close  of  the  Paleozoic 
era.  A,  Appalachia;  B,  Triassic  basin  or  do  wn  warp; 
(7,  Appalachian  Mountains. 

Lower  figure:  The  same  region  as  it  now  appears  after 
much  erosion,  the  submergence  of  Appalachia,  and  the 
deposition  of  the  Coastal  Plain  beds.  A,  Coastal  Plain; 
B,  Piedmont  Plateau;  C,  Appalachian  Mountains. 
(By  W.  J.  Miller.) 

larities  began  to  be  carved  out  by  the  work  of  erosion  so  that  even 
from  early  youth  the  mountains  presented  a  rugged  surface. 
Mountains  now  in  process  of  growth,  like  the  Coast  Ranges  of 


THE  PERMIAN  PERIOD 


California,  show  such  ruggedness.  The 
great  thrust  faults,  especially  of  the  south- 
ern Appalachians  where  certain  great  rock 
masses  have  been  pushed  for  miles  over 
others,  were  not  produced  by  single  move- 
ments but  rather  by  many  repeated  move- 
ments along  the  same  thrust  planes  (see 
Fig.  113). 

Important  orogenic  movements  from 
Newfoundland  to  Rhode  Island,  and  also 
ji  the  Ouachita  Mountains  of  Arkansas, 
are  regarded  as  having  taken  place  at  the 
same  time.  Accordingly  the  whole  eastern 
side  of  the  continent  was  profoundly  af- 
fected by  mountain-making  disturbances. 

Other  important  geographic  changes 
in  addition  to  the  above  were  (1)  the 
warping  of  the  surface  of  Appalachia  as 
we  shall  show  in  our  discussion  of  the 
Triassic  period;  (2)  the  uplift  of  the  Mis- 
sissippi Basin,  mostly  without  folding  of 
the  strata,  east  of  the  Great  Plains  never 
again  to  become  submerged  to  the  pres- 
ent time  except  along  the  Gulf  Coast  ;  and 
(3)  the  elevation  and  erosion  of  most  of 
the  Permian  areas  west  of  the  Rocky 
Mountains  in  the  United  States,  which 
thus  accounts  for  a  pretty  widespread  un- 
conformity between  the  Permian  and 
Triassic  in  those  areas. 


O  Catf:  S- 

JM  I  § 

?f  ~1 

II  ^   p   £•. 


, 

5-      tb  &. 


<    H    CD 

1.11^ 
P*1! 


. 

£»  S.I'  w 

O    02  fT  * 

*  £  S  >>  era 

Pf       '.I     H. 

ttr 


FOREIGN  PERMIAN 

Europe.  —  The  Permian  of  Europe 
also  shows  two  rather  distinct  phases  — 
marine  and  non-marine  —  but  the  system 
in  central  and  western  Europe  is  usually 
separated  from  the  underlying  Upper  Car- 
boniferous (Pennsylvanian)  by  uncon- 
formity, thus  presenting  a  contrast  to 


^o 


a^- 


>-  g  S, 
s  ^  o 


J?JP| 


188  HISTORICAL  GEOLOGY 

North  America.  Early  in  the  Permian  a  great  salt  lake  (or  series 
of  lakes),  sometimes  with  local  fresh-water  conditions,  extended 
over  western  to  central  Europe  from  Ireland  to  central  Germany. 
Red  beds,  consisting  of  sandstones,  shales,  marls,  salt  and  gypsum, 
together  with  some  coal  beds,  were  formed  in  these  inland  water 
bodies.  Fossils  prove  that  marine  waters  sometimes  spread  over 
at  least  portions  of  this  inland  basin.  Glacial  deposits  have  re- 
cently been  discovered  toward  the  base  of  the  Permian  in  Ger- 
many. Another  feature  of  special  interest  is  the  large  amount  of 
igneous  rock  in  the  form  of  lava  flows,  dikes,  and  tuffs  in  the  Lower 
Permian,  particularly  in  the  British  Isles,  Germany,  France,  and 
the  Alps. 

Where  the  Lower  Permian  occurs  in  southern  Europe,  it  is 
mostly  of  marine  origin. 

About  the  beginning  of  the  Upper  Permian,  marine  waters 
appear  to  have  prevailed  over  the  enclosed  basin  areas  of  central 
and  western  Europe,  but  soon  again  those  waters  withdrew  to 
restore  salt  lake  conditions  (Fig.  114).  Neither  coal  nor  igneous 
rock  occurs  in  the  Upper  Permian,  but  the  greatest  salt  beds  in  the 
world  were  deposited  in  northern  Germany  during  late  Permian 
time.  Some  layers  of  magnesium  and  potassium  salts  were  depos- 
ited with  the  common  salt,  one  well  having  penetrated  the  deposit 
near  Berlin  to  a  depth  of  4000  feet  without  reaching  the  bottom. 

Upper  Permian  rocks  do  not  occur  in  France,  and  where  found 
in  southern  Europe  they  are  largely  marine. 

In  Russia,  the  type  region  for  the  Permian,  rocks  of  this  age 
underlie  much  of  the  country  and  appear  at  the  surface  over  a  wide 
area  in  the  eastern  part,  just  east  of  the  Ural  Mountains.  These 
rocks  are  usually  conformable  upon  the  Upper  Carboniferous 
(Pennsylvanian) .  Non-marine  deposits,  including  red  beds  with 
salt  and  gypsum,  are  common,  though  at  some  horizons  true 
marine  strata  prove  incursions  of  the  sea. 

Other  Continents.  —  In  many  other  parts  of  the  world  Permian 
rocks  are  extensively  developed,  particularly  in  northern  Asia, 
China,  Persia,  northern  India  (including  the  Himalayas),  South 
Africa,  Australia,  Tasmania,  New  Zealand,  Argentina,  and  Brazil. 
Continental  deposits  are  common.  A  most  remarkable  feature  is 
the  widespread  occurrence  of  thick  (sometimes  from  1000  to  2000 
feet)  glacial  deposits  in  the  Permian  system  in  low-latitude  coun- 
tries such  as  India,  South  Africa,  southern  Brazil,  and  Australia. 


THE  PERMIAN  PERIOD 


189 


Furthermore,  the  plain  inference  from  the  close  association  of 
certain  of  these  glacial  deposits  with  marine  strata  is  that  glaciers 
near  the  equator  came  down  near  or  actually  to  sea-level. 


Fig.  114 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  during 
later  Permian  time.  The  lighter  shading  represents  chiefly  lagoon  areas, 
while  the  heavier  shading  shows  areas  of  marine  water.  (After  De  Lap- 
parent,  from  Chamberlin  and  Salisbury's  "Geology,"  courtesy  of  Henry 
Holt  and  Company.) 

In  some  countries,  as  South  Africa,  Brazil,  and  Australia,  coal 
beds  also  occur  within  the  Permian. 

CLIMATE 

From  the  above  descriptions  it  is  evident  that  the  Permian 
presents  a  remarkable  combination  of  climatic  conditions,  includ- 
ing extensive  glaciation,  widespread  aridity,  and  conditions 
favorable  for  prolific  growth  of  coal-forming  plants,  all  in  a  single 


190  HISTORICAL  GEOLOGY 

period.  Thus  the  climate  of  the  Permian  stands  out  in  striking 
contrast  against  the  mild  and  uniform  climate  of  the  immediately 
preceding  period.  The  concentration  of  the  extensive  glaciation 
over  low-latitude  countries,  instead  of  high-latitude  regions,  is  at 
present  without  adequate  explanation.  It  must  be  confessed  that 
the  perplexing  problems  of  Permian  climate  are  as  yet  far  from 
solved. 

ECONOMIC  PRODUCTS 

As  already  suggested,  coal  beds  of  considerable  economic 
importance  occur  in  the  Permian  of  the  northern  Appalachian 
belt,  France,  Germany,  Bohemia,  Australia,  Transvaal,  and  Brazil. 

Salt  is  obtained  from  the  Permian  strata  of  Kansas,  Oklahoma, 
and  central  Europe. 

Gypsum  deposits,  which  are  so  widespread  in  rocks  of  Permian 
age,  are  quarried  in  many  states  as  Iowa,  Kansas,  Oklahoma, 
Texas,  New  Mexico,  South  Dakota,  and  Colorado.  There  are  also 
important  gypsum  and  potash  deposits  in  Europe. 

LIFE  OF  THE  PERMIAN 

As  compared  with  the  preceding  Paleozoic  periods,  the  Permian 
shows  a  decided  decrease  in  numbers  and  diversity  of  organisms. 
The  known  animal  species  of  the  period  are  to  be  reckoned  by  hun- 
dreds only.  The  organisms  of  the  Permian  were  in  several  ways 
distinctly  transitional  in  character  between  those  of  the  Paleozoic 
and  Mesozoic  eras. 

Plants.  —  All  the  principal  groups  of  Cryptogams  were  repre- 
sented much  as  in  the  Pennsylvanian,  except  that  the  Lycopods 
were  very  greatly  reduced.  In  fact  the  Lepidodendrons  became 
wholly  extinct  by  the  dose  of  the  period.  The  Equisetce  and 
Ferns  continued  to  be  prominent,  the  Tree-ferns  particularly 
becoming  more  common. 

From  the  standpoint  of  evolution,  the  most  interesting  changes 
or  advances  occurred  among  the  Gymnosperms.  In  addition  to 
the  Cordaites,  which  continued  from  the  Pennsylvanian,  Cycads 
and  Conifers  are  known  for  the  first  time,  thus  giving  the  flora  a 
decided  Mesozoic  aspect. 

Protozoans.  —  Foraminifers  continued  to  be  very  abundant  as 
shown  by  their  presence  in  marine  limestones.  Radiolarians  were 
present  though  they  are  not  well  known  as  fossils. 


THE  PERMIAN  PERIOD  191 

Porifers  were  present  though  they  are  not  common  in  fossil 
form. 

Co3lenterates.  —  An  important  change  took  place  in  the  evolu- 
tion of  the  Corals  because  of  the  first  appearance  of  more  modern 
Hexacoralla,  or  forms  whose  septa  or  dividing  walls  were  six  in 
number  or  multiples  of  six.  The  Paleozoic  Tetracoralla,  however, 
still  continued  to  be  common. 

Echinoderms.  —  So  far  as  the  records  show,  this  sub-kingdom 
diminished  in  an  extraordinary  manner,  though  Crinoids,  Aster  o- 
zoans,  and  Echinoids  were  present. 

Molluscoids.  —  Bryozoans  were 
abundant. 

Brachiopods  continued  to  be  com- 
mon with  straight-hinged  types,  so 
abundant  through  the  Paleozoic  era, 
still  prevalent  for  the  last  time. 

Mollusks.  —  Pelecypods  continued 
to  increase  in  numbers  and  species, 
while  Gastropods  much  like  the  older 
Paleozoic  forms  were  still  common. 

Cephalopods.  —  Some   early    Pale-  Fig.  115 

ozoic  types  of  Nautiloids  (e.g.  Orthoc-  A  Permian  chambered  Cephalo- 
eras  and  Gyroceras)  still  persisted  and      ^^Z™^ 
various  species  of  the  modern  genus      folded     suture     (partition) 
Nautilus  were  added.    The  Ammonoids      lines, 
show  the  most  interesting  evolutionary 

changes,  because  of  the  notably  increased  complexity  of  their 
partition  or  suture  structures.  A  good  example  is  shown  in  Fig. 
115  which  is  really  more  suggestive  of  Mesozoic  Ammonites  than 
of  Paleozoic  Nautiloids. 

Arthropods.  —  Among  the  Crustaceans  and  Arachnids  the 
groups  of  Trilobites  and  Eurypterids  became  extinct.  In  fact  they 
had  but  few  representatives  in  the  Permian. 

Insects  have  been  found  in  abundance,  especially  in  the 
Permian  of  Kansas  and,  though  the  species  are  different,  they 
were  much  like  those  of  the  Pennsylvanian. 

Vertebrates.  —  Fishes  were  in  general  very  similar  to  those  of 
the  Mississippian  and  Pennsylvanian,  though  there  were  various 
species  and  genera  changes. 
C  Amphibians.  —  In  general  it  may  be  said  that  the  Permian 


HISTORICAL  GEOLOGY 


Fig.  116 

A  Permian  Reptile,  Pareiasaurus  serrideus.  This  creature  reached  a  length  of 
over  8  feet.  (After  Broom,  from  Chamberlin  and  Salisbury's  "Geology," 
courtesy  of  Henry  Holt  and  Company.) 


Fig.  117 

A  Permian  Reptile  (Pelycosaurian),  Naosaurus  claviger.     (After  Osborn, 
from  Scott's  " Geology,"  permission  of  The  Macmillan  Company.) 


THL  PERMIAN  PERIOD  193 

Amphibians  were  much  like  those  of  the  Pennsylvanian,  except 
that  some  were  even  larger,  new  species  were  added,  and  even  more 
reptilian  features  were  developed  in  some. 

Reptiles.  —  Any  possible  doubt  about  the  existence  of  true 
Reptiles  in  the  Pennsylvanian  is  completely  removed  when  we 
consider  the  abundant  reptilian  records  of  the  Permian.  They 
developed  in  a  remarkable  manner,  so  that  before  the  close  of  the 
period  several  important  subclasses  or  orders,  represented  by 
many  individuals,  were  evolved.  Some  of  the  Reptiles  already 
began  to  show  pretty  distinct  mammalian  characteristics.  The 
accompanying  figures  will  give  a  good  idea  of  two  important 
Permian  forms. 


CHAPTER  XIII 

SUMMARY    OF    PALEOZOIC    HISTORY 

"WE- have  defined  geology  as  the  history  of  the  evolution  of 
the  earth.  -  Evolution,  therefore,  is  the  central  idea  of  geology. 
It  is  this  idea  alone  whichmakes  geology  a  distinct  science.  This^ 
is  the  coherent  principle  which  unites  and  gives  significance  to  all 
the  scattered  facts  of  geology  —  which  cements  what  would  other- 
wise be  a  mere  incoherent  pile  of  rubbish  into  a  solid  and  symmetri- 
cal edifice.  It  seems  appropriate,  therefore,  that  at  the  end  of  the 
long  and  eventful  Paleozoic  era  we  should  glance  backward  and 
briefly  recapitulate  the  evidences  of  progressive  change  (evolu- 
tion)."1 

PALEOZOIC  ROCKS 

Paleozoic  rocks  are  dominantly  sandstones,  conglomerates, 
shales,  and  limestones  of  typical,  marine,  sedimentary  character, 
though  continental  deposits  also  are  common,  such  as  fresh-water, 
swamp,  or  lagoon  deposits  of  the  Pennsylvanian  in  the  eastern 
Mississippi  Basin  and  the  "Red  Beds"  formed  in  great  salt  lakes 
of  Permian  age  in  the  southwestern  United  States. 

The  marine  strata  furnish  abundant  evidence,  by  the  presence 
of  ripple  and  wave-marks,  the  coarseness  of  the  clastic  materials 
(conglomerates  and  sandstones),  etc.,  that^thev_were  deposited  in 
shallow  (epicontinental)  seas,  and  "never  in  really  deep  ocean 
water.  Continental  deposits  are  also  abundantly  represented. 

In  Europe  the  estimated  maximum  thickness  of  Paleozoic  strata 
is  75,000  to  100,000  feet.  It  must  be  remembered,  however,  that 
this  does  not  mean  that  such  a  great  thickness  of  strata  is  present 
in  any  one  locality,  but  rather  that  this  represents  the  sum-total 
of  the  greatest  thicknesses  of  the  different  formations  of  the  con- 
tinent. 

A  thickness  of  more  than  25,000  feet  of  strata  (largely  clastic) 
actually  piled  layer  upon  layer  may  now  be  seen  exposed  in  the 

1  J.  LeConte:  Elements  of  Geology,  5th  Ed.,  p.  421. 
194 


SUMMARY  OF  PALEOZOIC   HISTORY  195 

highly  folded  and  eroded  Appalachians,  while  the  maximum 
thickness  of  strata  there  must  be  between  40,000  and  50^DDy  feet. — 

The  Paleozoic  group  of  rocks  in  the  interior  ol  the  Mississippi 
Basin  measures  only  a  few  thousand  feet  in  thickness,  and  lime- 
stones are  there  relatively  more  abundant  than  clastic  deposits, 
because  of  the  generally  greater  distance  from  the  eroding  lands. 

In  the  western  United  States,  Paleozoic  strata  usually  show  a 
thickness  of  many  thousands  of  feet,  and  limestones  are  there 
also  prominently  developed. 

The  only  large  masses  of  igneous  rocks  of  Paleozoic  age  are 
Mississippian  or  Pennsylvanian  or  both  in  the  northern  Cordilleras 
and  in  parts  of  New  England. 

PHYSICAL  HISTORY 

Relations  of  Land  and  Sea. — Throughout  the  Paleozoic  era  the 
most  persistent  lands  were  large  portions  of  northeastern  North 
America;  Appalachia,  the  large  area  which  occupied  the  eastern 
side  of  the  United  States;  and  islands  and  land  areas  of  varying 
positions  and  sizes  in  the  Cordilleran  region.  Most  of  the  Missis- 
sippi Basin  and  much  of  the  western  side  of  the  continent  were 
submerged  under  epicontlnental  seas  during  the  greater  portion 
of  the  time.  There  were  many  oscillations  of  level  of  the 
land,  or  rising  or  falling  of  the  sea-level,  or  both,  causing  re- 
peated emergence  and  submergence  of  small  and  large  areas.  In 
this  summary  only  the  most  salient  geographic  changes  will  be 
mentioned.  The  paleogeographic  maps  should  be  reviewed.  Also 
the  accompanying  generalized  map  (Fig.  118)  should  be  studied. 

The  era  opened  with  much  of  North  America  a  land  area,  but 
early  in  the  Cambrian  marine  waters  extended  across  the  southern 
portion  of  the  United  States  and  northward  by  estuaries  through 
both  the  Appalachian  and  Rocky  Mountain  districts.  Throughout 
Cambrian  time  and  to  mid-Ordovician,  a  progressive  submergence 
took  place  reaching  a  climax  with  all  the  continent  submerged 
except  two  or  three  land  areas  around  Hudson  Bay,  Appalachia, 
and  some  islands  in  the  west.  In  late  Ordovician  time  came  emer- 
gence of  considerable  areas  followed  by  extensive  submergence 
which  reached  a  climax  toward  the  middle  of  the  Silurian  with 
nearly  as  much  of  the  continent  under  water  as  during  the  mid- 
Ordovician.  Similar  extensive  emergence  at  the  beginning,  and 


196 


HISTORICAL  GEOLOGY 


widespread  submergence  toward  the  end  of  the  period,  charac- 
terized both  the  succeeding  Devonian  and  Mississippian.     The 


Fig.  118 

Highly  generalized  paleogeographic  map  of  North 
America  during  the  Paleozoic  era.  White  areas 
were  the  more  persistent  lands  (positive  elements); 
lined  and  dotted  areas  were  the  more  persistent  waters; 
dotted  areas  were  the  principal  geosynclines.  (Some- 
what modified  by  W.  J.  M.  after  Charles  Schuchert.) 

Pennsylvanian  was  characterized  by  marine  conditions  in  the  west 
and  low-lying,  swampy  lands  in  the  east.  During  Permian  time 
nearly  all  of  eastern  North  America  was  dry  land,  and  alternating 


SUMMARY  OF  PALEOZOIC  HISTORY  197 

salt-like,  lagoon,  and  marine  conditions  prevailed  in  the  south- 
eastern United  States. 

Through  the  era  the  emergences  and  submergences  of  great 
areas  affected  the  western  part  of  the  continent  less  than  the 
eastern,  as  proved  by  the  fact  that  the  strata  there  show  fewer 
unconformities  and  are  rich  in  limestone,  thus  indicating  greater 
persistence  of  oceanic  conditions,  especially  from  the  Ordovician 
to  the  Mississippian  inclusive.  Of  all  the  west,  the  Great  Basin 
region  appears  to  have  been  the  most  continuously  submerged. 

Mountain  Making.  —  During  the  era  there  were  only  two  times 
of  great  orogenic  movements  in  North  America  when  thick  masses, 
of  strata  were  subjected  to  lateral  compression  and  upraised  into 
mountain  ranges.  The  first  of  these  was  toward  the  close  of  the 
Ordovician  when  the  Taconic  Mountain  range  was  formed  along 
— theTeastern  border  of  the  continent  just  east  of  the  present  site  of 
the  Appalachians.  The  second  was  toward  the  close  of  the  era 
(Permian)  when  one  of  the  greatest  post-Algonkian  physical  dis- 
turbances in  the  history  of  North  AmericaTresu»ltedIn  the  formation 
of  the  Appalachian  Mountains  by  folding  and  faulting  of  the  strata. 

Vulcanism.  —  The  long  Paleozoic  era  was  remarkably  free  from 
igneous  activity  in  North  America,  the  only  extensive  intrusions 
and  extrusions  of  igneous  rocks  having  taken  place  during  the 
Mississippian  (and  probably  Pennsylvania^  in  the  northern 
Cordillera.  Some  intrusions  occurred  in  eastern  Canada  during 
Silurian  and  probably  Devonian  time.  Other  intrusions,  usually 
regarded  as  of  Carboniferous  age  (either  Mississippian  or  Pennsyl- 
vanian),  occurred  in  Massachusetts. 

In  Europe,  however,  igneous  activity  was  more  frequent  and 
widespread  during  the  era. 

CLIMATE 

The  strongest  evidence  from  the  character  and  distribution  of 
the  organisms  points  to  a  temperate  and  pretty  uniform  climate  for 
most  part  over  the  globe  during  Paleozoic  time. 

Typical  glacial  deposits  show  that  extensive  areas  were  glaci- 
ated about  the  beginning  of  the  early  Cambrian  and  again  toward 
the  close  of  the  era  (Permian) . 

Certain  deposits  such  as  the  "Red  Beds,"  salt,  and  gypsum 
indicate  at  least  local  arid  climate  conditions,  as  for  example  in 


TABULAR  SUMMARY  OF  PALEOZOIC  LIFE 


Plants 

Protozoans 

Porifers  and 
Ccelenterates 

Echinoderms 

PERMIAN 

Thallophytes. 
Bryophytes\ 
Pteridophytes:  Ly- 
copods     reduced  ; 
Equisetse  and  Ferns 
prominent. 
Gymnosperms:   Com- 
mon,   e.g.      Cycads, 
Cordiates,  Conifers. 

Foraminifers: 
Very  common. 

Radiolarians: 
Present. 

Sponges:  Present. 

Corals:  Ancient  Te- 
tracoralla  still  com- 
mon, but  first  Hex- 
acoralla  appear. 

Crinoids:  Greatly  di- 
minished. 

Asterozoans:        Pres- 
ent. 

Echinoids:    Present. 

PENNSYL- 

VANIAN 

Thallophytes. 
Bryophytes. 
Pteridophytes:      Cul- 
minate,   e.g.     Lyco- 
pods,  Equisetae  and 
Ferns. 
^Seed-f  erns)  . 
Gymnosperms:     Sim- 
ple    ones     common 
e.g.  Cordaites. 

Foraminifers: 
Very       abun- 
dant. 

Radiolarians: 
Present. 

Sponges:  Present. 

Corals:     Similar    to 
Mississippian  but 
less  common. 

/ 

Blastoidfe:  Become 
extinct. 
Crinoids:     Declining. 

Asterozoans:   Pres- 
ent. 

Echinoids:  Rare. 

MISSISSIP- 

PIAN 

\ 

Thallophytes. 
Sryophytes. 
Pteridophytes:    Com- 
mon and  much  like 
Devonian. 
(Seed-ferns). 

Gymnosperms  :  Simple 
types  only  present. 

Foraminifers: 
Very  abun- 
dant. 

Radiolarians: 
Common. 

Sponges:  Common. 
Graptolites:  Very 
rare  and  become  ex- 
tinct. 
Corals:    Cup  and 
Honey-comb  forms 
only,  and  less  prom- 
inent  than   in    the 
Devonian. 

Blastoids:   Culminate 
and    become    nearly 
extinct. 
Crinoids:     Culminate 
in  numbers  and  spe- 
cies. 
Asterozoans:    Not 
common. 
Echinoids:    Common. 

DEVONIAN 

Thallophytes:    Sea- 
weeds and  Diatoms. 
Bryophytes? 
Pteridophytes:   Lyco- 
pods,  Equiseta?,  and 
Ferns. 
(Seed-ferns). 
Gymnosperms:     Sim- 
ple types  only. 

Foraminifers: 
Present. 

iadiolarians: 
Present. 

Sponges:   Common. 
Graptolites:  Decline 
almost  to  extinction. 

Corals:   Cup  and 
Honey-comb  forms 
greatly  increased  in 
numbers   and   size; 
Chain  corals  rare 
and  become  extinct. 

Cystoids:     Rare    and 
become  extinct. 
Blastoids:      Still    un- 
common. 
Crinoids:       Still      in- 
creasing. 
Asterozoans:      Abun- 
dant. 
Echinoids:  Present. 

SILURIAN 

Thallophytes:   Sea- 
weeds. 

Bryophytes? 

Pteridophytes: 
Ferns,  but  rare. 

Foraminifers: 
Present. 

Eladiolarians: 
Present. 

Sponges:  Common. 
Graptolites:    Dimin- 
ished   in    numbers 
and  species. 
Corals:     Increase  in 
prominence  and 
Chain-corals    be- 
come nearly  extinct. 

Cystoids:  Prominent. 
Blastoids:   Still  rare. 

Crinoids:    Increase  in 
numbers  and  species. 

Asterozoans  and 
Echinoids:  Increase. 

ORDOVICIAN 

j|j 

Thallophytes: 
Sea-weeds. 

Higher    Cryptogams? 

Foraminifers: 
Abundant. 

Eladiolarians: 
Abundant. 

Sponges:  Very  com- 
mon. 
Graptolites:     Reach 
climax  in.  numbers 
and  species. 

Corals:  Common  e.g. 
Cup,   Honey-comb, 
and  Chain  forms. 

Cystoids:   Culminate. 

Blastoids:     First    ap- 
pear and  rare. 
Crinoids:      First    ap- 
pear and  common. 
Asterozoans  and 
Echinoids:   First  ap- 
pear and  rare. 

CAMBRIAN 

Thallophytefc: 
Algae. 

Foraminifers: 
Present. 

Sponges:  Common. 
Elydrozoans  :    Giap- 
tolites     and     Jelly- 
fishes,     both    com- 
mon. 

Corals:  Present? 

Cystoids:      Primitive 
forms  and  rare. 

TABULAR  SUMMARY  OF  PALEOZOIC  LIFE —Continued 


Molluscoids 

Mollusks 

Arthropods 

Vertebrates 

Bryozoans: 
Abundant. 

Brachiopods:    Still 
common,  with  new 
species;    straight; 
hinged    forms    still 
prevail. 

Pelecypods:    Greatly    in- 
creased in  numbers  and 
species. 
Gastropods:  Common. 
Cephalopods:  Some  earlier 
forms    still   persist,    but 
Ammonoids  (e.g.  Waag- 
enoceras)   now   common 
and  more  complex. 

Trilobites:  Very  rare  and 
become  extinct. 
Eurypterids: 
Become  extinct. 

Insects:    Much  like  the 
Pennsylvanian. 

Fishes   and    Amphib- 
ians: Much  like  the 
Pennsylvanian,     but 
with  new  species.            Q 

Reptiles:    Many  rep- 
resentatives   of    the 
lower  orders. 

Bryozoans: 
Common. 

Brachiopods:     Still 
declining,  but 
fairly  common; 
straight-hinged 
forms  prevail. 

Pelecypods:    Still  increas- 
ing. 
Gastropods:  Common  and 
first  land  forms  appear. 
Cephalopods:    Similar  to 
Mississippian,  but  Nauti- 
loids declining  and  Am- 
monoids more  complex. 

Trilobites:  Rare. 
Eucrustaceans:  Present. 
Arachnids:     Eurypterids 
still  declining;  first  Spi- 
ders appear. 
Myriapods:  Common. 
Insects:      Common     and 
large;       simpler     types 
only. 

Fishes:      Much     like 
Mississippian. 
Amphibians:  Culmin-    « 
ate,  e.g.  Stegocepha-     \  ***• 

lans.                          « 

Reptiles:  Present? 

Bryozoans:   More 
abundant    than    in 
the  Devonian. 
Brachiopods:    De- 
clining but  still 
common  and  with 
many  new  species; 
mostly  straight- 
hinged  forms. 

Pelecypods:     More    com- 
mon than  before. 
Gastropods:  Common. 
Cephalopods:    Much  like 
the  Devonian,  but  coiled 
Nautiloids  culminate 
and  Ammonoids  are 
more  complex. 

Trilobites:  Rare. 
Eucrustaceans? 
Arachnids:     Eurypterids 
declining. 

Myriapods:  Present. 
Insects:  No  fossils. 

Fishes:  Selachians  in- 
creasing;    Dipnoans             , 
declining;    Arthrodi- 
rans  declining;  Gan-       '•'**  *• 
oids    increasing. 

Amphibians:  Present. 

Bryozoans:  Present. 

Brachiopods  ^    Cul- 
minate in  numbers 
and  species;   many 
new  forms  added; 
mostly  straight- 
hinged  forms. 

Pelecypods    and    Gastro- 
pods: Much  like  the  Si- 
lurian. 
Cephalopods  :  Most  earlier 
forms   persist,   but  Am- 
monoids first  appear,  e.g. 
Goniatite. 

Trilobites: 
Decline  markedly. 
Eucrustaceans  :  Common. 
Arachnids:     Eurypterids 
declining,  but  still  not- 
able for  size.               , 
Myriapods:  First  known. 
Insects:    Unknown, 

Ostracoderms:  Culmi- 
nate     and     become 
extinct. 
Fishes:  Very  .profuse, 
e.g.  Selachians,              i.    <-   ' 
Dipnoans,  Arthrodi- 
rans  and  Ganoids. 
Amphibians?     > 

Bryozoans: 
Abundant. 

Brachiopods:  Prom- 
inent in  numbers 
and  species;  nearly 
all    straight-hinged 
forms. 

Pelecypods    and    Gastro- 
pods: Common  and  much 
like  Ordovicidn. 
Cephalopoda  Common 
and   much   like  Ordovi- 
cian,  but  coiled   Nauti- 
loids predominate. 

Trilobites:       Diminished 
but  still  common. 
Eucrustaceans:      Similar 
to  Ordovician. 
Arachnids*   First   Scorp- 
ions ;  Eurypterids  culmi- 
nate in  numbers,  species 
and  size  (?). 

Ostracoderms:    Rare, 
small  and  primitive. 

Fishes:     Selachians         L  '  I 
of   primitive  charac-      ^ 
ter  and  rare. 

Bryozoans: 
Abundant. 

Brachiopods:    More 
complex,  larger.and 
abundant  ;    Articu- 
lates prevail;    and 
nearly  all  are 
straight-hinged 
forms. 

Pelecypods:     Larger  and 
more  common. 
Gastropods:  Common. 
Cephalopods:  Very  prom- 
inent and  all  are  Nauti- 
loids,    e.g.     Orthoceras, 
Cyrtoceras,  Trochoceras 
and  Trocholites. 

Trilobites:    Culminate  in 
numbers  and  species. 
Eucrustaceans:  Few  and 
.simple. 

Eurypterids:  Present. 

Ostracoderms:  Mark- 
ing first  appearance       -     j 
of  Vertebrates;  speci-. 
mens  rare  and  very 
fragmentary. 

Bryozoans:  Absent. 

Brachiopods:  Small, 
thin-shelled;    Inar- 
ticulates  prevail; 
some  Articulates  in 
the  Upper  Cam- 
brian. 

Pelecypods:     Very    small 
and  rare* 
Gastropods:  Rare*  simple 
and  mostly  in  the  Upper 
Cambrian. 
Cephalopods:  Rare,  small 
and   simple;,  all   Ifauti- 
loidse.g.,  Orthoceras  and 
Cyrtoceras. 

Crustaceans:     Trilobites 
common     and     usually 
highly    segmented    and 
with   small   tail   plates; 
some  very  simple  forms. 
Eurypterids:   Rare. 

None. 

200  HISTORICAL  GEOLOGY 

northern  Siberia  (Ordovician) ;  New  York  (Salina  epoch  of  the 
Silurian);  Michigan,  Montana,  Nova  Scotia,  and  Australia 
(Mississippian) ;  and  southwestern  United  States,  western  and 
central  Europe,  and  other  parts  of  the  world  (Permian). 

ORGANIC  HISTORY 

Viewed  in  a  broad  way,  the  life  of  the  Paleozoic  is  distinctly 
different  from  that  of  the  succeeding  Mesozoic  or  Cenozoic.  Very 
few  species  and  not  many  genera  passed  from  the  Paleozoic  to  the 
Mesozoic,  and  even  the  larger  groups  of  organisms  which  did  con- 
tinue usually  underwent  important  structural  changes.  Paleozoic 
organisms  were  the  more  primitive  in  structure,  and  it  has  been 
aptly  said  that  they  bear  somewhat  the  same  relation  to  the  suc- 
ceeding forms  that  the  embryo  does  to  the  adult. 

Of  plants  in  the  early  Paleozoic  only  the  simplest  Cryptogams 
are  known,  while  in  the  later  Paleozoic  periods  there  are  abundant 
records  of  the  higher  Cryptogams  such  as  Lycopods,  Equisetae, 
and  Ferns,  as  well  as  of  the  Gymnosperms.  Angiosperms  (typical 
flowering  plants)  are  wholly  unknown  from  the  Paleozoic,  and  even 
the  later  forests  and  foliage  of  the  era  must  have  presented  a  gloomy 
appearance  because  of  the  lack  of  true  flowering  plants  as  com- 
pared with  today. 

The  animals  of  the  Paleozoic  were  predominantly  inverte- 
brates, though  Fishes  were  common  in  the  Devonian  and  later 
periods,  and  Amphibians  and  Reptiles  appeared  in  the  later  periods. 
Among  the  most  common  and  characteristic  types  of  invertebrates 
were  Graptolites,  Corals,  stemmed  Echinoderms  (Pelmatozoans), 
Bryozoans,  Brachiopods,  Tetrabranch  Cephalopods  (Nautiloids 
especially),  Trilobites,  and  Eurypterids.  Certain  of  the  higher 
Arthropods  such  as  Spiders,  Myriapods  (Centepedes),  and  Insects 
did  not  appear  till  the  era  was  pretty  well  advanced. 

The  accompanying  chart  has  been  devised  by  the  writer  for  the 
purpose  of  bringing  together  the  salient  facts  in  the  organic  history 
of  the  Paleozoic  era.  Period  by  period  the  principal  evolutionary 
changes  in  the  subkingdoms  and  classes  of  plants  and  animals  are 
graphically  represented. 


THE   MESOZOIC   ERA 


CHAPTER  XIV 

THE    TRIASSIC    PERIOD 
OKIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

THE  name  "Triassic"  was  given  because  of  the  threefold, 
extensive  development  of  the  rocks  of  the  system  where  first 
studied  in  Germany.  It  so  happens,  however,  that  the  German 
Triassic  strata  are  not  typical  of  the  system,  as  shown  by  later 
studies  in  other  parts  of  the  world. 

The  following  table  gives  a  general  idea  of  the  main  sub- 
divisions in  North  America  and  Europe: 


Pacific  Coast 
(Various  formations} 

Atlantic  Coast 

Germany 

TRIASSIC  (  Upper  T^ssic  series. 
SYSTFM  {  Middle  Triassic  series. 

OYo  1  -Ejjyi     1      -r                          rr\     • 

1  Lower  Inassic  series 

Newark  series. 

Keuper  series. 
Muschelkalk  series. 
Bunter  series. 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  The  accompanying  map  (Fig.  119) 
shows  the  surface  distribution  of  both  the  Triassic  and  Jurassic 
rocks  in  North  America.  The  Atlantic  Coast  areas  are  wholly 
Triassic ;  the  California  areas  are  mostly  Jurassic ;  and  the  remain- 
ing areas  include  both  Triassic  and  Jurassic  rocks  which  have 
usually  not  been  carefully  separated.  There  is  no  reason  whatever 
to  believe  that  Triassic  rocks  were  ever  deposited  over  Canada 
except  along  the  western  coast  and* to  a  slight  extent  in  Nova 
Scotia.  Likewise  it  is  not  known  that  Triassic  rocks  ever  occurred 
in  the  Mississippi  Basin  except  immediately  west  of  the  Rocky 

201 


202 


HISTORICAL  GEOLOGY 


tf 


Fig.  119 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Triassic  and 
Jurassic  strata  in  North  America.  Some  areas  of  doubtful  age  and  extent 
not  shown  in  British  Columbia.  All  Atlantic  Coast  areas  are  Triassic.  In 
much  of  the  western  United  States  the  Triassic  and  Jurassic  have  not  yet 
been  satisfactorily  separated.  (By  W.  J.  M.,  data  from  two  maps  by 
Bailey  Willis,  U.  S.  Geological  Survey.) 


THE  TRIASSIC  PERIOD 


Mountains.  This  is  in  marked  contrast  with 
the  Paleozoic  systems.  Accordingly,  the 
present  concealed  Triassic  rocks  and  areas 
of  their  former  presence  are  pretty  largely 
confined  to  the  immediate  regions  of  exist- 
ing outcrops. 

Rocks  of  the  Atlantic  Coast.  — These 
rocks  (Newark  series)  are  seen  on  the  map 
to  occupy  comparatively  small,  narrow  areas 
just  east  of  and  parallel  to  the  Appalachian 
Mountain  range  from  southeastern  New 
York  to  South  Carolina,  and  farther  north- 
ward in  the  Connecticut  River  Valley  and  in 
Nova  Scotia.  In  the  northern  areas  the 
rocks  are  sandstones  and  shales,  with  some 
coarse  conglomerates,  especially  at  the  base. 
Because  of  their  prevailing  red  color  and 
general  resemblances  to  the  "Old  Red  Sand- 
stone" (Devonian)  of  Scotland,  they  have 
been  called  the  "New  Red  Sandstone." 
Many  of  the  beds  show  sun-cracks,  rain- 
drop pits,  ripple-marks,  and  foot-prints,  and 
remains  of  land  Reptiles  (Dinosaurs).  In 
Virginia  and  the  Carolinas  the  rocks  have 
a  similar  lithologic  character,  though  the  red 
color  is  not  so  common,  and  some  workable 
coal  beds  occur.  The  fossils,  which  are 
mostly  plants  in  the  dark  shales,  point  to 
the  Upper  Triassic  age  of  the  Newark  series. 

The  rocks  of  the  series  are  nearly  every- 
where somewhat  folded,  tilted,  and  exten- 
sively fractured  by  normal  faults,  and  they 
also  contain  numerous  lava  flows,  intrusive 
sheets,  and  dikes  of  so-called  trajTrock  (dia- 
base) (Figs.  120, 121).  A  remarkable  feature 
is  the  great  thickness  of  the  rocks  in  these 
narrow  belts,  fully  3000  feet  in  Virginia; 
7000  to  10,000  feet  in  the  Connecticut 
Valley;  and  10,000  to  15,000  feet  in  New 
Jersey. 

Rocks  of  the  Western  Interior.  —  The 
Trisssic  strata  of  the  western  interior  region 
are  distributed  over  nearly  the  same  areas 
as  the  Permian,  and  in  many  places  the  rocks 


ill 


204 


HISTORICAL  GEOLOGY 


of  these  two  systems  are  not  at  all  sharply  separated.  All  the 
known  Triassic  rocks  of  the  western  interior  are  located  within  the 
shaded  area,  indicating  continental  deposits  on  map  Fig.  123.  Red 
Beds  (sandstones  and  shales),  similar  to  those  of  the  underlying 
Permian  and  often  with  salt  and  gypsum  beds,  are  the  most  com- 
mon rocks  (Fig.  122).  They  are  certainly  very  largely  of  conti- 
nental origin.  Their  thickness  varies  from  100  to  200  feet  in  the 


Fig.  121 

Tilted   and   faulted   Triassic   sandstone  in   the   Connecticut 
Valley  near  Northampton,  Mass.    (W.  J.  Miller,  photo.) 

eastern  part  of  the  western  interior  to  2000  or  more  feet  in  Utah. 
In  the  Rocky  Mountains  the  strata  of  this  age  are  often  highly 
tilted  or  folded,  while  just  east  of  the  Rockies  they  are  generally 
nearly  horizontal. 

Rocks  of  the  Pacific  Coast.  —  These  are  the  only  true  Marine 
Triassic  rocks  of  North  America,  and  they  are  there  extensively 
developed  with  practically  all  portions  of  the  system  from  oldest 
to  youngest  well  represented,  particularly  in  California  and 
Nevada.  The  rocks  consist  mostly  of  shales,  slates,  limestones, 
conglomerates,  and  sandstones,  usually  several  thousand  feet  thick 
and  with  a  maximum  thickness  of  17,000  feet  in  Nevada  and  13,000 
feet  in  British  Columbia.  In  Alaska  and  British  Columbia  the 
system  contains  much  igneous  material. 


System 


Oligocene 


Jurassic 


Permian 


Pennsylvania!! 


Ordovician 


Cambrian 


Pre-Cambrian 


Kind  of  Rock 


sand  and  gravel 


gray  shale 
limestone 


dark 

shale 

and 

sandy-shale 


red  and  buff 
sandstone 

gray  and  buff 
shale 


Columnar 
Section 


red  and  buff 

sandstone  and 

shale 


red  shale 
and  gypsum 


limestone  and 
red  sands 


white  sandstone 

gray  to  red 
limey  sandstone 


red  shale 


gray 
limestone 


pink  limestone 


shale 
sandstone 


schist,  granite 


I  ,     I.I 


J ,1       .1 


ill 


j I.I 


Thickness 
in  Feet 


25-150 


1390 


325-590 


325 


500+ 


100-120 


500+ 


650 


80 


100-300 


II 
" 


O 


I 


l! 

w  =2 


206  HISTORICAL  GEOLOGY 

Thickness  of  the  System  and  Igneous  Rocks.  —  Figures  show- 
ing the  thickness  of  the  system  in  different  parts  of  the  continent 
have  already  been  given.  Igneous  rocks  are  abundant  only  in 
British  Columbia,  Alaska,  and  also  in  the  Newark  series  of  the 
Atlantic  Coast,  the  last  named  being  again  referred  to  below. 


PHYSICAL  HISTORY 

Atlantic  Coast.  —  Accompanying  map  Fig.  123  shows  the  geog- 
raphy of  the  continent  during  Triassic  time,  though  it  must  be 
borne  in  mind  that  the  areas  of  deposition  along  the  Atlantic  Coast 
were  such  only  in  the  latter  part  of  the  period. 

The  non-marine  strata  (Newark  series)  of  Upper  Triassic  age 
clearly  show  by  their  present  distribution  and  mode  of  occurrence 
that  they  were  deposited  in  a  series  of  long,  trough-like  depressions 
whose  trend  was  parallel  to  that  of  the  main  axis  of  the  Appalachian 
range.  These  troughs  lay  between  the  Appalachians  proper  and 
old  Appalachia,  which  latter  was  then  also,  in  part,  made  up  of  the 
greatly  worn  down  Taconic  Mountains.  The  fact  that  these 
troughs  are  true  downwarps,  and  that  they  so  perfectly  follow  the 
trend  of  the  Appalachian  folds,  makes  it  certain  that  they  were 
formed  by  a  great  lateral  pressure  which  was  a  continuation  of  the 
Appalachian  disturbance.  Thus  the  Appalachian  Mountains  still 
seem  to  have  been  growing  well  into  the  Triassic  period  and,  while 
the  Paleozoic  strata  were  being  folded,  the  surface  of  old  Appa- 
lachia, including  part  of  the  Taconic  region,  was  also  more  or  less 
warped,  the  downwarps  forming  the  troughs  in  which  the  Triassic 
beds  were  deposited.  These  depressions  or  troughs  were  most 
favorably  situated  for  rapid  accumulation  of  thick  deposits  be- 
cause of  their  position  immediately  between  the  two  great  land 
masses  which  were  being  eroded.  The  sediments  derived  from 
the  erosion  of  the  young  Appalachians  were  especially  abundant 
because  of  the  vigorous  wearing  down  of  these  newly  formed 
mountains.  Thus  the  great  thickness  of  the  Newark  series  is 
accounted  for.  Their  thickness  strongly  argues  for  a  gradual 
downwarping  of  the  basins  as  the  deposition  of  sediments  went  on. 
It  is  often  stated  that  these  strata  were  formed  in  estuaries,  but  the 
presence  of  sun-cracks,  ripple-marks,  Reptile  tracks,  etc.,  show 
that,  in  part  at  least,  the  beds  may  have  formed  in  very  shallow 


THE  TRIASSIC  PERIOD 


207 


Fig.  123 

Paleogeographic  map  of  North  America  during  Triassic  time.  Note  the 
extensive  areas  of  continental  deposition.  (Slightly  modified  after  Bailey 
Willis,  courtesy  of  The  Journal  of  Geology.} 


208  HISTORICAL  GEOLOGY 

water,  such  as  flood-plains  or  lakes,  where  changing  condition 
frequently  allowed  the  surface  layers  to  lie  exposed  to  the 
sun. 

"The  curiously  shaped  and  often  huge  Reptiles  of  that  age 
(Triassic)  wandered  over  the  mud  exposed  at  low  tide,  and  their 
foot-prints,  being  covered  by  the  deposit  of  the  next  flood  tide, 
constitute  the  so-called  'Bird  tracks'  which  have  been  found  in 
such  great  numbers  and  perfection."  1 

During  the  time  of  the  formation  of  the  Newark  beds,  there  was 
considerable  igneous  activity,  as  shown  by  the  occurrence  of  sheets 
of  igneous  rocks  within  the  mass  of  sediments.  In  some  cases  true 
lava  flows  with  cindery  tops  were  poured  out  on  the  surface  and 
then  became  buried  under  later  sediments,  while  in  other  cases  the 
sheets  of  molten  rock  were  forced  up  either  between  the  strata  or 
obliquely  through  them,  thus  proving  their  intrusive  character. 
As  a  result  of  subsequent  erosion,  these  igneous  rock  masses  often 
stand  out  conspicuously  as  topographic  features.  Perhaps  the 
most  noteworthy  of  these  is  the  great  igneous  rock  sheet,  part  of 
which  outcrops  to  form  the  Palisades  of  the  Hudson  River,  and 
which  altogether  outcrops  for  a  distance  of  70  miles.  The  molten 
rock  first  broke  through  the  strata  and  then  crowded  its  way  along 
parallel  to  them.  Another  fine  example  is  the  so-called  Holyoke 
Range  of  Massachusetts  (Fig.  124)  regarding  which  Emerson  says: 
"The  accumulation  of  sediments  was  interrupted  by  an  eruption 
of  lava  through  a  fissure  in  the  earth's  crust,  which  opened  along 
the  bottom  of  the  basin.  The  lava  flowed  east  and  west  on  the 
bottom  of  the  bay,  as  tar  oozes  and  spreads  from  a  crack,  and  solidi- 
fied in  a  sheet  which  may  have  been  2  or  3  miles  wide  and  about 
400  feet  thick  in  its  central  part.  This  is  the  main  sheet  or  Holyoke 
diabase.  The  sheet  was  soon  covered  with  sand  layers,  but  its 
thickness  was  such  that  it  had  shallowed  the  waters  to  near  tide 
level,  and  thus  occasioned  extensive  mud  flats."  2  In  both  regions 
just  mentioned,  the  contraction  of  the  cooling  masses  often  ex- 
pressed itself  by  breaking  the  rock  into  great  and  small,  crude, 
nearly  vertical  columns,  and  hence  the  application  of  the  term 
"palisades."  The  steep  mountain  sides  or  cliffs  are  due  to  the  fact 
that  the  hard  igneous  rock  is  much  more  resistant  to  weathering 
and  erosion  than  the  sandstone  above  and  below  it  (Fig.  124). 

1  B.  K.  Emerson:  U.  S.  G.  S.,  Holyoke  folio  No.  50,  p.  3. 

2  Ibid.,  Folio  No.  59,  p.  3. 


THE  TRIASSIC  PERIOD 


209 


Western  Interior.  —  The  large  area  of  sedimentation  in  this 
part  of  the  continent  had  little  or  no  connection  with  marine 
waters.  Conditions  of  deposition  of  later  Permian  time  appear  to 
have  been  continued  through  Triassic  time,  that  is,  continental 
deposits  were  formed  mostly  in  salt  lakes,  fresh  lakes,  and  along 
stream  courses,  while  some  may  even  have  been  wind-blown. 

Pacific  Coast.  —  Since  fossils  show  the  strata  of  the  Pacific 
Coast  to  be  chiefly  of  marine  origin,  it  is  evident  that  sea  water 


Fig.  124 

The  steep  western  front  of  the  Holyoke  Range  as  seen  from 
Easthampton,  Massachusetts.  The  upper  portion  is 
columnar  lava  of  Triassic  age,  and  this  rests  upon  Tri- 
assic red  sandstone.  (W.  J.  Miller,  photo.) 

spread  over  the  areas  where  these  strata  now  occur  (see  map  Fig. 
123).  Igneous  rocks  in  the  Triassic  of  British  Columbia  prove  that 
there  was  considerable  vulcanism  there  during  the  period. 

Close  of  the  Triassic.  —  The  Triassic  closed  in  eastern  North 
America  with,  crustal  disturbances  which  raised  the  basins  of  depo- 
sition of  the  Newark  series  into  dry  land,  thus  leaving  all  of  the 
eastern  half  or  two-thirds  of  the  continent  dry  land  and  undergoing 
erosion  for  the  first  time  since  the  beginning  of  the  Paleozoic  era. 

On  the  Pacific  Coast  the  evidence  is  pretty  clear  that  marine 
conditions  continued  as  during  the  period,  while  in  the  western 
interior  the  geographic  conditions  toward  the  close  of  the  Triassic 


210  HISTORICAL  GEOLOGY 

are  as  yet  more  doubtful  because  scarcity  of  fossils  renders  a  sepa- 
ration of  possible  Jurassic  strata  from  Triassic  uncertain.  The  best 
evidence,  however,  points  to  continual  deposition  of  "Red  Beds" 
over  some  of  the  region  at  least. 


FOREIGN  TRIASSIC 

Europe.  —  As  in  America,  so  in  Europe,  the  Triassic  shows 
considerable  development  of  both  continental  and  marine  facies. 
The  Bunter  series  (1600  to  1800  feet  thick)  of  Germany  consists 
chiefly  of  red  beds,  such  as  sandstones  and  shales,  with  some  salt 
and  gypsum,  clearly  indicating  deposition  under  arid  climate  con- 
ditions much  like  the  western  interior  of  the  United  States  at  the 
same  time.  The  Muschelkalk  of  Germany  is  mostly  a  marine 
limestone  formation  up  to  1000  feet  thick,  thus  showing  the  pres- 
ence of  marine  waters  over  the  region,  probably  as  an  arm  of  the 
sea,  similar  to  the  Baltic  Sea,  as  the  fossils  suggest.  During  part 
of  this  time,  at  least,  salt  lake  conditions  were  restored  as  indicated 
by  gypsum  and  salt  in  the  midst  of  the  series.  During  Keuper 
time  conditions  of  deposition  were  much  as  during  the  Bunter, 
though  marine  waters  again  transgressed  the  area  toward  the  close 
of  the  Triassic. 

In  England,  much  of  eastern  Russia,  and  western  and  southern 
Spain,  Triassic  strata  essentially  like  those  of  Germany  are  well 
developed. 

In  middle  southern  Europe  the  marine  facies  is  widely  devel- 
oped, being  mostly  limestone  (often  dolomitic)  and  shales.  The 
rugged  peaks  of  the  famous  "Dolomites"  or  Tyrolean  Alps  have 
been  carved  out  of  this  comparatively  resistant  dolomitic  limestone, 
much  of  which  was  of  Coral-reef  origin. 

Map  Fig.  125  gives  a  good  idea  of  the  relations  of  land  and 
water  in  Europe  during  earlier  Triassic  time. 

Other  Continents.  —  The  marine  facies  of  the  European  Tri- 
assic continues  eastward  through  much  of  southern  Asia,  there 
being  an  unusually  fine  development  of  the  system  in  the  Hima- 
layas. Triassic  rocks,  sometimes  of  continental  origin,  also  occur 
in  other  parts  of  Asia  as  in  Japan  and  eastern  Siberia. 

Triassic  rocks  are  also  known  in  Australia,  New  Zealand,  north 
and  south  Africa,  and  South  America,  with  coal-bearing  strata  in 
Argentina  and  Chile,  and  marine  strata  in  the  Andes. 


THE  TRIASSIC  PERIOD 


211 


CLIMATE 

The  extensive  areas  of  "Red  Beds,"  often  accompanied  by 
salt  and  gypsum,  in  the  western  interior  and  eastern  North  Amer- 
ica, northern  and  western  Europe,  and  northern  Africa  show  wide- 
spread aridity  of  climate  in  the  northern  hemisphere  during  the 


Fig.  125 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  in  the  early 
Triassic.  Full  lines  =  marine  waters;  broken  lines  =  areas  of  non-marine 
deposition.  (After  De  Lapparent,  from  Chamberlin  and  Salisbury's  "Ge- 
ology," courtesy  of  Henry  Holt  and  Company.) 

period.  There  is  no  evidence  of  glaciation,  and  the  fossils  indicate 
mildness  of  climate.  Judging  by  the  character  and  distribution  of 
the  fossils,  the  water  of  the  Arctic  Sea  was  appreciably  cooler  than 
that  of  lower  latitudes,  so  that  climatic  zones  must  have  been 
defined  to  some  extent  at  least. 


212  HISTORICAL  GEOLOGY 

ECONOMIC  PRODUCTS 

Coal  beds  of  some  commercial  value  occur  in  the  Triassic  rocks 
of  Virginia  and  North  Carolina. 

Enormous  quantities  of  sandstone  (the  so-called  "Triassic 
Brownstone")  for  building  purposes  have  been  quarried  from  the 
Newark  series,  especially  in  the  Connecticut  River  Valley. 

Gypsum  of  Triassic  age  is  quarried  in  some  of  the  western 
states. 

Some  copper  deposits  occur  in  Triassic  rocks  of  California  and 
Alaska. 

LIFE  OF  THE  TRIASSIC 

The  physical  revolution  which  closed  the  Paleozoic  era  was 
accompanied  by  one  of  the  most  profound  changes  in  organisms 
in  the  earth's  history,  and  hence  we  may  expect  the  life  of  the 
Triassic  to  have  been  very  notably  different  from  that  of  preceding 
time.  Some  types  of  animals  and  various  types  of  plants  continued 
from  the  late  Paleozoic,  but  the  general  aspect  of  Triassic  life  was 
distinctly  more  modern  than  that  of  the  Paleozoic.  In  spite  of 
this  comparatively  rapid  evolutionary  change  in  both  fauna  and 
flora,  enough  connecting  links  are  known  to  make  sure  that  the 
Mesozoic  animals  and  plants  were  derived  from  the  Paleozoic. 

Plants.  —  Triassic  plants  have  not  left  us  a  very  abundant 
record.  In  fact  the  rather  widespread  aridity  of  climate  doubt- 
less hindered  a  luxuriant  growth,  over  wide  areas  at  least. 

Among  the  simple  plants  (Thallophytes)  the  calcareous  Sea- 
weeds, that  is  those  which  had  the  power  to  secrete  limey  skeletons, 
were  especially  common. 

Among  Pteridophytes  the  Ferns  and  their  allies  were  still  im- 
portant; the  Equisetce  were  fairly  common,  though  much  more  like 
the  existing  forms  except  for  their  greater  size;  and  the  Lycopods 
were  reduced  almost  to  extinction,  even  the  few  lingering  Sigil- 
larians  having  finally  disappeared  with  this  period,  so  that  the 
Lycopods  will  not  again  call  for  special  mention. 

Gymnosperms  were  the  dominant  types  of  plants  of  the  Tri- 
assic, just  as  Pteridophytes  had  been  the  dominant  plants  of  the 
later  Paleozoic.  The  Cordaites  were  greatly  reduced  and  they  be- 
came extinct  during  this  period.  Cycads  and  their  allies  and  the 
Conifers  (Fig.  126),  however,  were  the  most  common  elements  of 


THE  TRIASSIC   PERIOD 


213 


the  flora.  Fig.  135  gives  a  good  idea  of  a  modern  Cycad,  though 
it  must  be  understood  that  such  plants  are  today  relatively 
unimportant. 

It  is  generally  stated  that  the  plants  of  the  Triassic,  except 
toward  the  close  of  the  period,  in  both  Europe  and  America  pre- 
sented  a  stunted  or 
dwarfed  appearance  on 
account  of  unfavorable 
(chiefly  climatic)  en- 
vironment. Such  an  im- 
poverished condition  of 
Triassic  plants  was  at 
least  not  universal,  for 
as  Knowlton  says:  "In 
North  Carolina,  Virginia, 
and  Arizona  there  are 
trunks  of  trees  preserved, 
some  of  which  are  8  feet 
in  diameter  and  at  least 
120  feet  long,  while  hun- 
dreds are  from  2  to  4  feet 
in  diameter.  Many  of 
the  Ferns  are  of  large 
size,  indicating  luxuriant 
growth."  1 

Protozoans  and  Pori- 
fers  were  present,  though 
their  records  are  neither 
very  abundant  nor  of 
special  interest. 

Crelenterates.  —  For 
the  first  time  the  Hexa- 
coralla,  or  forms  of  mod- 
ern   aspect,    became    abundant,    while    the   ancient    (Paleozoic) 
Tetracoralla  dwindled  away  to  extinction. 

Echinoderms.  —  Crinoids   were    common,    the   more   ancient 
types  having  given  way  to  those  of  more  modern  aspect. 

Asterozoans  were  present. 

Echinoids   (Sea-urchins)   were  common,   though  most  of  the 
1  F.  H.  Knowlton:  Jour.  Geol,  Vol.  18,  1910,  p.  106. 


Fig.  126 

Parts  of  a  Triassic  Conifer,  Voltzia  hetero- 
phylla.  (After  Fraas  from  Scott's  "Ge- 
ology," courtesy  of  The  Macmillan  Com- 
pany.) 


214 


HISTORICAL  GEOLOGY 


dominant  Paleozoic  types  were  gone  and  all  were  forms  of  regular 
shape.  For  the  first  time  the  Echinoids  were  more  prominent  than 
the  Crinoids. 

Molluscoids.  —  Bryozoans  continued,  but  with  certain  impor- 
tant genera  changes. 

Brachiopods  showed  two  important  changes,  namely  (1)  a  great 
reduction  in  number  of  species  and  of  individuals,  and  (2)  the  shells 

with  straight-hinge  lines  becoming  sub- 
ordinate to  those  with  curved-hinge  lines 
for  the  first  time,  a  common  genus  (Tere- 
bratula)  of  the  latter  being  represented 
by  a  Cretaceous  form  in  Fig.  159.  To 
the  present  day  the  Brachiopods  never 
again  became  conspicuous  elements  of  the 
fauna.  In  spite  of  the  important  changes, 
a  few  of  the  Paleozoic  genera  survived  the 
transition  to  the  Mesozoic. 

Mollusks. — This  subkingdom  included 
all  of  the  most  abundant  invertebrate 
animals  of  the  period,  all  of  the  well- 
known  classes  having  been  prominently 
represented. 

Pelecypods  were  more  numerous  and 
diversified  than  ever  before.     They  vastly 
outnumbered    the  Brachiopod  bivalves. 
Certain  still  existing  genera  were  intro- 
duced so  that  many  forms  were  of  decided  modern  appearance. 
Gastropods.    Several    Paleozoic    genera   existed    for   the    last 
time,  and  certain  more  modern  types  appeared. 

Cephalopods.  Among  the  Nautiloids  the  straight-shelled 
form  (Orthoceras),  known  from  the  very  early  Paleozoic,  became 
extinct  in  the  Triassic,  while  the  coiled  forms  were  still  common  and 
much  like  those  of  later  Paleozoic  time. 

Among  the  Ammonoids  an  evolutionary  feature  of  particular 
interest  was  the  development  of  still  greater  complexity  of  shell 
structure.  Goniatite-like  forms  still  persisted,  but,  even  early  in 
the  Triassic,  forms  with  slightly  serrated  sutures  or  partition 
structures  (e.g.  Ceratites,  Fig.  127)  appeared.  Later  in  the  period 
representatives  of  the  most  complex  of  all  known  chambered 
Cephalopods,  that  is  the  Ammonites,  appeared  (see  Fig.  141). 


Fig.  127 

A  Triassic  Ceratite,  Cera- 
tites trojanus,  with  part 
of  shell  removed  to  show 
suture  structure.  (After 
J.  P.  Smith,  slightly 
modified  by  accentua- 
tion of  sutures.) 


THE  TRIASSIC   PERIOD 


215 


Another  important  advance  among  the  Cephalopods  was  the 
first  appearance  of  the  Dibranchs,  which  include  the  highest  of  all 
Mollusks.  Of  these  Dibranchs  perhaps  the  most  characteristic 
belonged  to  a  group  known  as  Belemnites  (see  Fig.  143),  though 
these  were  not  abundant.  A  fuller  discussion  of  the  Dibranchs 
will  be  given  in  the  next  chapter. 

Arthropods.  —  Among  Crustaceans  neither  Trilobites  nor  Eu- 
rypterids,  so  important  in  the  Paleozoic,  continued  into  the  Meso- 
zoic,  but  the  Eucrustaceans  showed  a  notable 
advance  by  the  first  appearance  of  the  so-called 
long-tailed  Decapods  (Macrura)  or  Lobster 
family,  which  rank  among  the  highest  of  all 
Crustaceans  (Fig.  128). 

Insects  also  showed  distinct  progress  by  the 
addition  of  the  Beetle  tribe,  which  ranks  next 
to  the  highest  of  all  insects. 

Fishes. — Selachians,  Dipnoans,  and  Ganoids 
(Fig.  129)  all  continued  with  the  Ganoids  pre- 
dominant. Teleosts  had  not  yet  appeared. 

Amphibians.  —  Though  somewhat  dimin- 
ished as  compared  with  the  later  Paleozoic,  the 
Amphibians  were  still  numerous  and  often  not- 
able for  their  great  size.  In  general  they  were 
much  like  the  late  Paleozoic  forms.  Mastodon- 
saurus  attained  a  length  of  15  or  20  feet  and 
had  a  skull  4  feet  long.  The  Bunter  series  of 
Germany  is  particularly  rich  in  fine  fossil  Am- 
phibians. By  the  close  of  the  Triassic  the 
Amphibians  had  declined  remarkably,  so  that 
among  the  land  Vertebrates,  of  which  they  were  the  ancestors, 
they  never  again  assumed  a  position  of  importance. 

Reptiles.  —  Because  of  the  great  abundance,  size,  and  variety 
of  Reptiles,  the  Mesozoic  era  is  often  called  the  "  Age  of  Reptiles." 
Even  in  the  Triassic  most  of  the  more  important  and  interesting 
now  extinct  groups  had  appeared,  such  as  the  swimming  Reptiles 
(e.g.  Enaliosaurs) ;  walking  Reptiles  (e.g.  Dinosaurs);  and  flying 
Reptiles  (e.g.  Pterosaurs).  Since  these  remarkable  reptilian  forms 
reached  their  climax  of  development  later  in  the  Mesozoic,  a  fuller 
discussion  will  be  reserved  for  a  subsequent  chapter.  In  passing, 
however,  it  may  be  mentioned  that  Dinosaurs,  often  of  great  size, 


Fig.  128 

A  Triassic  long- 
tailed  Macruran 
Decapod,  Pern- 
phi  x  Sueurii. 
(From  Naumann.) 


216 


HISTORICAL  GEOLOGY 


Fig.  129 

A  Ganoid,  Catopterus  redfieldi,  from  the  Triassic  sandstone  of  Connecticut. 
(After  Newberry,  U.  S.  Geological  Survey,  Monograph  14.) 

were  the  creatures  which  left  the  numerous  foot-prints  up  to  15  or 
18  inches  in  length  in  the  Newark  sandstone  of  the  Connecticut 
Valley  (Figs.  130,  131). 


X 


Fig.  130 

Tracks  of  a  small  two-legged  Dinosaur  on  a  slab  of  Triassic 
sandstone  from  the  Connecticut  Valley.  The  tracks 
are  about  4  inches  long.  (W.  J.  Miller,  photo.) 

Of  the  more  modern  reptilian  forms,  the  Turtles  and  Lizards 
made  their  first  appearance,  the  latter  only  in  late  Triassic  time, 
but  none  of  them  became  common. 


THE  TRIASSIC  PERIOD  217 

Mammals.  —  Another  very  important  step  in  the  development 
of  animal  life  was  the  introduction  of  Mammals  in  the  Triassic 


Fig.  131 

Tracks  of  a  large  two-legged  Dinosaur  on  Triassic  sandstone  from  the  Con- 
necticut Valley,  showing  how  both  feet  slid  some  distance  in  the  soft  ma- 
terial after  which  the  creature  suddenly  sat  down,  the  end  of  the  backbone 
having  left  a  distinct  impression.  (After  Edward  Hitchcock.) 

period.  Although  Mammals  include  the  most  highly  developed  of 
all  animals,  their  earliest  representatives  (in  the  Triassic)  were 
very  small,  primitive  types,  apparently  not  very  numerous,  thus 


218  HISTORICAL  GEOLOGY 

scarcely  suggesting  their  later  (Cenozoic)  development  into  the 
manifold  and  most  powerful  and  intelligent  creatures  of  the  earth. 
Only  a  few  genera  are  known  from  the  Triassic,  and  in  fact  Mam- 
mals continued  to  occupy  a  very  subordinate  position  throughout 
the  Mesozoic  era. 


CHAPTER  XV 


THE    JURASSIC    PERIOD 
ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

THE  rocks  of  Jurassic  age  are  of  peculiar  interest  because  they 
comprise  one  of  the  very  first  systems  whose  subdivisions  were 
carefully  determined  by  the  use  of  fossils,  this  work  having  been 
done  in  England  about  one  hundred  years  ago  by  William  Smith, 
who  is  often  called  the  father  of  historical  geology.  Smith  applied 
the  name  " Oolitic"  to  the  system  because  of  the  common  occur- 
rence of  so  much  oolitic  limestone,  but  this  term  later  gave  way  to 
the  term  "  Jurassic,"  so-called  from  the  Jura  Mountains,  between 
France  and  Switzerland,  where  the  rocks  of  the  system  are  un- 
usually well  exhibited  and  have  been  much  studied.  In  Germany, 
too,  much  study  has  been  devoted  to  this  system,  largely  because 
of  the  abundance  of  well-preserved  and  interesting  fossils. 

In  western  North  America,  where  the  only  undoubted  Jurassic 
strata  occur  on  this  continent,  the  subdivisions  of  the  system  are 
not  so  well  known  and  correlated,  so  that  various  more  or  less  local 
formation  names  are  still  employed.  The  following  table  gives  a 
summary  of  the  principal  subdivisions  for  three  important  regions : 


Pacific  Coast  of 
North  America 

England 

Germany 

f  Upper  Jurassic. 
JURASSIC  j  ,T.  ,  „    T 
SYSTEM]  Middle  Jurassic. 

(  Lower  Jurassic. 

Upper  Oolite. 
Middle  Oolite. 
f  Lower  Oolite. 
\  Lias. 

Malm  (or  White  Jura). 
Dogger  (or  Brown  Jura). 
Lias  (or  Black  Jura). 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  Except  in  Mexico  and  western  Texas, 
rocks  of  undoubted  Jurassic  age  are  wholly  confined  to  the  western 

219 


220 


HISTORICAL  GEOLOGY 


. 
3 


t 


if 


e« 

«-* 


part  of  the  continent.1  On  map  Fig.  119  the  considerable  areas 
shown  in  California  and  western  Nevada  are  mostly  Jurassic  rocks. 
Some  areas  are  also  definitely  known  in 
southern  Alaska  and  in  western  Oregon. 
In  the  western  interior  numerous  small 
areas  of  mostly  late  Jurassic  rocks  only  are 
known  from  northern  Arizona  and  north- 
western Colorado  northward  through  Idaho, 
Wyoming,  western  South  Dakota,  and 
Montana.  Rocks  of  late  Jurassic  age  also 
quite  certainly  occur  in  western  British 
Columbia  east  of  the  Cascade  Mountains. 

As  compared  with  all  preceding  systems 
since  the  early  Paleozoic,  rocks  of  the  Juras- 
sic system  are  the  least  extensively  devel- 
oped on  the  continent. 

Character  of  the  Rocks.  —  The  Jurassic 
rocks  of  California  and  Nevada,  and  the 
southern  coast  of  Alaska,  are  chiefly  of 
marine  origin  representing  much  or  all  of 
the  period.  In  the  Sierras  and  Coast 
Ranges  the  strata  are  usually  metamor- 
phosed and  highly  folded  (e.g.  Mariposa 
slates  of  the  Sierras,  Fig.  132). 

In  the  western  interior  Triassic  and 
Jurassic  strata  have  often  not  been  satis- 
factorily separated,  and  some  "Red  Beds" 
(with  gypsum)  of  continental  origin,  like 
those  of  the  Permian  period,  are  probably 
of  Jurassic  age.  At  any  rate,  the-  only 
known  true  marine  (Jurassic)  strata  in 
that  whole  region  are  of  late  Jurassic  age. 
These  rocks,  which  comprise  all  types  of 
ordinary  sediments,  especially  limestones 
and  slates,  are  usually  highly  folded  or 
tilted  in  the  Rockies,  Wasatch  Mountains, 
Black  Hills,  etc.,  and  hence  are  generally 
exposed  only  in  narrow  belts. 

1  Certain  non-marine  deposits  exposed  along  the  Potomac  River  in  Mary- 
land have  sometimes  been  called  Jurassic,  but  the  best  evidence,  as  presented 
by  W.  B.  Clark,  points  to  their  Comanchean  (Lower  Cretaceous)  age. 


&.S 

08    % 

II 

.S.S 


- 


^    o3  73 
o   ^   ^ 


II 


THE  JURASSIC  PERIOD  221 

Thickness  of  the  Jurassic.  —  The  thickness  of  the  system  in 
California  does  not  appear  to  be  over  2000  feet,  while  in  western 
Nevada  5000  to  6000  feet  of  limestones  and  slates  are  reported. 
In  Alaska  a  maximum  thickness  of  10,000  feet  has  been  found. 
Throughout  the  western  interior  the  thickness  never  appears  to  be 
great,  usually  not  more  than  a  few  hundred  feet. 

Igneous  Rocks.  —  Tremendous  bodies  of  granite  have  been 
intruded  into  rocks  as  young  as  the  late  Jurassic  (Mariposa)  slates, 
and  though  the  date  of  the  intrusion  is  not  certainly  known,  it 
very  likely  occurred  toward  the  close  of  the  Jurassic  period  and  as 
an  accompaniment  of  the  Sierra  Nevada  Revolution  (see  below). 

PHYSICAL  HISTORY 

Earlier  Jurassic  in  the  West.  —  During  this  time  nearly  all  of 
North  America  north  of  Mexico  was  a  land  area.  Marine  waters 
spread  over  western  Nevada,  most  of  California,  the  western 
coast  of  Oregon,  and  southern  Alaska.  The  western  interior  region 
received  only  continental  deposits,  probably  including  some  "Red 
Beds"  and  gypsum  in  moderate  amounts. 

Later  Jurassic  in  the  West.  —  In  the  latter  part  of  the  period 
western  Nevada  probably  was  not  covered  by  marine  waters,  but 
the  other  Pacific  Coast  regions  above  mentioned  were.  At  this 
same  time  an  important  change  took  place  in  the  western  interior 
region  by  a  transgression  of  the  sea  from  British  Columbia  south- 
ward over  the  Rocky  Mountain  district  to  northern  Arizona.  The 
accompanying  map  (Fig.  133)  shows  the  condition  of  the  continent 
at  that  time.  Eastern  Mexico  appears  to  have  been  largely  sub- 
merged also. 

Eastern  North  America  in  the  Jurassic.  —  No  Jurassic  strata 
now  occur  in  the  eastern  two-thirds  of  North  America  and  we  have 
no  evidence  that  any  ever  were  deposited  there,  hence  that  vast 
area  was  dry  land  undergoing  erosion  during  the  whole  period. 
The  period  was  ushered  in  by  a  slight  upwarping  of  the  Atlantic 
border  accompanied  by  some  faulting  and  tilting,  particularly  of 
the  Triassic  (Newark)  rocks,  as  shown  in  Fig.  120.  That  this  up- 
lift actually  occurred,  and  that  the  Jurassic  period  in  the  eastern 
United  States  was  a  time  of  extensive  erosion,  is  well  established, 
because  the  whole  Atlantic  seaboard,  including  the  tilted  and 
faulted  Triassic  strata,  was  worn  down  toward  the  condition  of  a 


222 


HISTORICAL  GEOLOGY 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONT1NENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAND 
LANDS 
INDETERMINATE  AREAS 


Fig.  133 

Paleogeographic  map  of  North  America  during  late  Jurassic  time.     (Slightly 
modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.} 


THE  JURASSIC   PERIOD  223 

peneplain  and  the  next  sediments  (Comanchean)  were  deposited 
upon  the  eastern  portion  of  that  worn-down  surface.  For  instance, 
on  Staten  Island  and  in  northern  New  Jersey,  the  Comanchean 
beds  may  be  seen  resting  directly  upon  the  deeply  eroded  Triassic 
rocks,  and  hence  the  proof  is  conclusive  that  during  much,  if  not 
all,  of  the  Jurassic  period  active  erosion  was  taking  place,  and  this 
in  turn  implies  that  the  Triassic  beds  were  well  elevated  in  the 
early  Jurassic. 

Close  of  the  Jurassic  (Sierra  Nevada  Revolution). — The 
close  of  the  period  witnessed  profound  geographic  changes  in  the 
western  part  of  the  continent.  During  both  the  Triassic  and 
Jurassic  periods,  as  well  as  throughout  much  of  Paleozoic  time, 
there  had  been  more  or  less  continuous  deposition  of  sediments  on 
the  Pacific  slope  over  the  sites  of  the  present  Sierra,  Cascade,  and 
Coast  Range  Mountains.  Toward  the  close  of  the  Jurassic  period 
these  thick  sediments,  particularly  in  the  Sierra  region,  were 
subjected  to  a  tremendous  force  of  lateral  compression,  the  strata 
being  upheaved,  folHed,  and  crumpled  (Fig.  132).  Thus  the  Sierra 
Nevada  Mountains  of  California  were  borne  out  of  the  ocean  and 
the  Pacific  shore  line  was  transferred  to  the  western  base  of  the 
newly  formed  range.  The  Sierras,  in  this  their  youth,  were  most 
likely  a  lofty  range,  but  were  later  much  worn  down  by  erosion, 
their  present  great  altitude  having  been  produced  by  later  (Ter- 
tiary) movements.  Accompanying  the  erogenic  movements,  the 
deeply  buried  sediments  were  metamorphosed  and  the  vast  quan- 
tities of  granite  were  probably  intruded  at  the  same  time,  this 
granite  being  now  exposed  to  view  only  because  of  profound  sub- 
sequent erosion.  As  a  result  of  the  metamorphism  the  thick 
Mesozoic  shales  were  converted  into  the  hard  (Mariposa)  slates. 

The  best  evidence  indicates  that  this  orogenic  disturbance  also 
affected  the  strata  of  the  Klamath  Mountains  in  northwestern 
California  and  the  Cascade  Mountain  region  through  Oregon, 
Washington,  and  even  British  Columbia. 

The  strata  then  occupying  the  site  of  the  present  Coast  Ranges 
were  somewhat  deformed,  but  probably  only  enough  "to  form  a 
chain  of  islands  or  a  very  low  mountain  range.  This  is  proved  by 
the  fact  that  Lower  Cretaceous  strata  are  found  resting  uncon- 
formably  upon  the  deformed  Jurassic  rocks.  The  orogenic  move- 
ments which  produced  the  Coast  Range  Mountains  as  we  now  see 
them  came  later.  Some  other  mountains  of  the  west,  such  as  the 


224 


HISTORICAL  GEOLOGY 


Humboldt  Range  of  western  Nevada,  were  also  probably  upraised 
toward  the  close  of  the  Jurassic. 

The  great  arm  of  the  sea  or  gulf  which  spread  over  the  western 
interior  region  late  in  the  Jurassic  was  drained  as  a  result  of  these 
crustal  disturbances.  Hence  we  learn  that  all  of  North  America 
except  much  of  the  western  margin  was  dry  land  at  the  close  of  the 
Jurassic  period. 

FOREIGN  JURASSIC 

Europe.  —  The  marine  transgression  which,  in  late  Triassic 
time,  resulted  in  the  submergence  of  the  great  salt  lakes  and  other 


Fig.  134 

Sketch  map  showing  the  relations  of  land  and  water  in 
Europe  during  late  Jurassic  time.  (Slightly  modified 
after  De  Lapparent.) 

basins  of  central  and  western  Europe,  continued  into  the  Jurassic. 
Even  in  the  early  (Lias)  part  of  the  period  the  sea  covered  consider- 
able areas  in  western,  central,  and  southern  portions  of  the  con- 
tinent. The  strata  are  mostly  typical  shallow  sea  sediments, 
though  some  coal-forming  swamps  existed  around  the  sea  borders 
in  central  Europe.  These  early  Jurassic  strata  are  usually  conform- 
able upon  and  not  sharply  separated  from  the  underlying  Triassic. 


THE  JURASSIC  PERIOD  225 

A  progressive  marine  transgression  continued  through  the 
middle  of  the  period  and  well  toward  its  close,  extending  farther 
and  farther  eastward,  till  much  of  the  continent  was  submerged, 
as  shown  by  Fig.  134.  This  was  one  of  the  greatest  marine  trans- 
gressions in  the  known  geological  history  of  Europe.  As  would  be 
expected,  the  strata  of  later  Jurassic  age  contain  much  more  lime- 
stone than  those  of  the  earlier  part  of  the  period,  because  of  the 
more  widespread  clear  water  areas.  During  all  this  time  the  great 
series  of  oolites  were  forming  in  England  and  the  famous  Solenhofen 
lithographic  limestone  was  being  deposited  in  southern  Germany. 

Just  before  the  close  of  the  period  a  considerable  retrogression 
of  ^the  sea  set  in,  draining  certain  areas  and  leaving  lakes  or  estu- 
aries in  certain  other  places. 

Other  Continents.  —  Jurassic  marine  strata  are  known  in 
many  places  in  Arctic  lands,  thus  showing  extensive  sea  waters 
of  that  time  there. 

A  great  marine  transgression  also  affected  Asia,  so  that  exten- 
sive areas  of  the  continent  became  submerged,  except  mostly  in 
the  central  portion.  Widespread  Jurassic  deposits  are  known  in 
Asia  Minor,  Siberia,  India  (especially  the  Himalayas),  Persia, 
Turkestan,  and  Japan. 

Jurassic  rocks  are  also  known  in  northern  and  eastern  Africa, 
western  South  America,  Australia,  and  New  Zealand. 

CLIMATE 

In  general  the  evidence  from  the  character  and  distribution  of 
the  organisms  shows  that  the  climate  was  comparatively  mild. 
Corals,  for  example,  had  a  range  several  thousand  miles  farther 
northward  than  they  do  today.  A  careful  study  of  the  migrations 
of  certain  animals  has,  however,  pretty  well  established  the  fact 
that  the  Arctic  Sea  was  notably  colder  than  the  Atlantic  and 
Pacific,  but  it  is  perhaps  too  much  to  say  that  the  northern, sea 
was  as  cold  as  it  is  now.  There  was  quite  certainly  some  definition 
of  climatic  zones,  especially  in  later  Jurassic  time. 

ECONOMIC  PRODUCTS 

Considerable  crude  oil  is  obtained  from  Jurassic  strata  in  south- 
ern California. 

The  great  gold-bearing  veins  or  lodes  of  the  famous  "  Mother 


226 


HISTORICAL  GEOLOGY 


Fig.  135 

A  living  Cycad,  Dioon  edule,  of    Mexico.     (From  a  photograph   by  Prof. 
C.  J.  Chamberlain.) 


THE  JURASSIC  PERIOD 


227 


Lode  Belt"  of  the  Sierra  Nevada  occur  in  Jurassic  and  older 
slates. 

In  California,  also,  important  quicksilver  deposits  occur  in 
metamorphosed  Jurassic  and  later  rocks. 

Coal  beds  of  some  importance  are  found,  mostly  in  the  Lower 
Jurassic,  in  Hungary,  various  parts  of  Asia,  and  Australia. 

As  already  mentioned,  the  famous  Solenhofen  lithographic 
stone  of  Bavaria  is  of  Jurassic  age. 

LIFE  OF  THE  JURASSIC 

In  Europe,  as  would  be  expected  because  of  the  great  sea  trans- 
gression, the  marine  life  was  prolific,  and  a  wonderfully  rich  record 
has  been  left  and  care- 
fully studied  by  many 
paleontologists.  Some 
idea  of  the  profusion 
of  marine  organisms 
may  be  gained  from 
the  fact  that  more  than 
4000  species  are  known 
from  the  British  Isles 
alone.  The  far  less  com- 
plete American  marine 
record  is  in  harmony 
with  the  adverse  phys- 
ical conditions. 

Beside  the  marine 
fossils,  the  wonderful 
records  of  land  animals, 
especially  the  remark- 
able and  now  extinct  Mesozoic  Reptiles,  are  worthy  of  particular 
mention. 

Plants.  —  Viewed  in  a  broad  way,  the  plants  of  the  Jurassic 
were  much  like  those  of  the  preceding  period,  though  some  pro- 
gressive evolutionary  changes  took  place.  Ferns,  Equisetce, 
Cycads  (Figs.  135, 136, 137),  and  Conifers  continued  to  be  the  domi- 
nant forms,  with  the  Cycads  attaining  their  culmination  in  both 
number  of  individuals  and  species.  The  Conifers  took  on  a  more 
modern  aspect.  The  flora  appears  to  have  been  remarkably  uni- 
form over  wide  portions  of  the  world. 


Fig.  136 

A  fossil  Cycad  tree  trunk,  Cycadeoidea  pukher- 
rima.  This  is  a  Lower  Cretaceous  species. 
(After  Darton  and  W.  S.  Smith,  U.  S.  Geo- 
logical Survey,  Folio  108.) 


228 


HISTORICAL  GEOLOGY 


Angiosperms  are  reported  to  have  been  represented  by  the 
Monocotyledons,  though  the  evidence  is  not  very  conclusive. 

Protozoans.  —  Foraminifers  and  Radiolarians  were  both  very 
abundant  and  highly  diversified.  Foraminifers  are  particularly 


Fig.  137 
Jurassic  Cycad  leaves.   (After  Ward,  U.  S.  Geological  Survey,  Monograph  48.) 


numerous  in  certain  Jurassic  clays,  while  certain  other  beds  of 
chert  or  jasper  are  almost  wholly  made  up  of  Radiolarian  shells. 

Porifers.  —  Sponges  were  very  abundant  and  diversified.  They 
are  often  beautifully  preserved,  even  to  the  minutest  details. 

Ccelenterates.  —  Anthozoans  (Corals)  continued  to  be  com- 
mon, and  all  were  of  the  modern  Hexacoralla  types. 


THE  JURASSIC  PERIOD 


229 


Echinoderms.  —  After  their  culmina- 
tion in  the  Mississippian,  the  Crinoids 
remained  in  a  comparatively  subordi- 
nate position  during  the  Permian  and 
Triassic  periods.  During  the  Jurassic 
they  again  became  profuse.  As  regards 
both  abundance  and  size  they  probably 
even  surpassed  those  of  the  Mississip- 
pian, though  not  in  diversity  of  species. 
Their  general  structure  was  more  like 
modern  forms  than  like  Paleozoic,  and 
also  there  is  good  evidence  that  the 
shallow-water  forms  so  common  in  the 
Paleozoic  began  to  give  way  to  deeper- 
water  forms  similar  to  those  so  prevalent 
today.  Fig.  138  gives  a  good  idea  of  one 
of  the  Jurassic  Crinoids,  the  highly  seg- 
mented and  delicately  branching  arms 
being  well  exhibited.  It  scarcely  seems 
credible  that  fully  600,000  segments 
have  been  counted  in  a  single  individual. 

Aster ozoans  were  moderately  represented  and  they  had  already 
assumed  a  distinctly  modern  structure. 

Echinoids.  —  These  forms,  which  first 
attained  much  prominence  in  the  Triassic, 
continued  to  increase  in  abundance  and 
variety  in  the  Jurassic.  Early  in  the  period 
regular  forms  only  existed,  but  later  in  the 
period  the  irregular  forms  made  their  first 
appearance.  The  regular  forms  were  radi- 
ally symmetrical,  while  the  irregular  ones 
were  only  bilaterally  symmetrical  (see  Figs. 
139,  140).  Since  the  latter  are  distinctly 
more  modern  in  structure,  we  have  here 
another  good  illustration  of  progressive 
evolution  toward  modern  forms. 

Molluscoids.  —  Bryozoans  were  present, 
but  apparently  not  very  important. 

Brachiopods  were  still  fairly  common, 
though  the  numbers  of  genera  and  species 


Fig.  138 
A    Jurassic    Crinoid,    Pen- 

tacrinus  fossilis.      (After 
Goldfuss.) 


Fig.  139 

A  regular  or  radially 
symmetrical  Echi- 
noid,  Pseudodiadema 
texanum,  of  Lower 
Cretaceous  age.  (Af- 
ter Hill  and  Vaughn, 
U.  S.  Geological  Sur- 
vey, Folio  76.) 


230 


HISTORICAL  GEOLOGY 


Fig.  140 

An  irregular  or  bilater- 
ally symmetrical  Echi- 
noid,  Hemiaster  tex- 
anus,  of  Cretaceous 
age.  (After  Hill  and 
Vaughn,  U.  S.  Geolog- 
ical Survey,  Folio  76.) 


were  reduced  to  only  a  few.  Most  of  these 
genera  have  continued  to  the  present  day, 
so  that  in  the  succeeding  periods  the  evolu- 
tion of  these  creatures,  so  very  prominent 
in  all  of  the  earlier  f  ossiliferous  periods,  has 
but  little  interest. 

Mollusks.  —  Pelecypods  were  even  more 
abundant  than  in  any  preceding  period, 
their  shells  often  largely  constituting  whole 
strata  or  thick  beds.  They  were  quite  mod- 
ern in  appearance,  many  genera  being  those 
which  still  exist.  The  members  of  the  Oyster 
family  were  most  common,  being  represented 
by  such  genera  as  Ostrea,  Exogyra,  Gryphea. 
Gastropods,  including  various  existing 
genera,  were  usually  common. 
Among  Cephalopods  the  ancient  and  important  straight-shelled 

Orthoceras  had  disappeared  with 

the  preceding  period,  but  coiled 

Nautiloids  still  were  common. 

The   Ammonoids   reached   the 

very  height  of  their  develop- 
ment in  the  Jurassic.     Among 

these,  the  most  characteristic 

and  abundant  were  the  Ammo- 
nites, in  which  the  sutures  or 

partition  structures  reached  the 

highest    degree   of    complexity 

(see  Fig.  141).    Many  hundreds 

of  species  are  known,  and  often 

Jurassic  strata  are  chiefly  com- 
posed of  them.     Of  all  coiled 

Cephalopods,  the  largest  were 

of  this  age,  some  Ammonites 

having  attained  a  diameter  of 

several   feet.    In    many    cases 

"  erratic    and    degenerate    de- 


velopments showed  themselves 
by  uncoiling  and  strange  coil- 
ing, presaging  a  stage  of  '  sport- 


Fig.  141 

An  Ammonite  with  part  of  shell  re- 
moved to  show  the  very  compli- 
cated (frilled)  sutures.  (From  Nor- 
ton's "Elements  of  Geology,"  by 
permission  of  Ginn  and  Company, 
Publishers.) 


THE  JURASSIC  PERIOD 


231 


ing'  and  retrogression  in  the  next  period,  followed  by  extinction" 

(Chamberlin  and  Salisbury).     The  reader  is  again  referred  to  the 

table  on  page  99  which  outlines  the  evolution 

of  the  chambered-shell  Cephalopods. 

We  learned  that  the  Dibranch  Cephalopods 

made    their    first    appearance   in   the   Triassic 

period.    In  the  Jurassic  these  forms  were  ex- 
ceedingly abundant  both  in  numbers  of  species 

and  of  individuals.     Most  characteristic  of  these 

were  the  Belemnites,  so-called  because  of  the 

long,    conical,    or   dart-shaped,   internal    shells 

which  are  generally  the  only  portions  preserved 
in  the  fossil  state  (see  Fig.  142). 
They  were  similar  in  appear- 
ance to  the  modern  Squids  or 
Cuttle-fishes.  Some  Jurassic 
forms  reached  a  length  of  over 
two  feet.  A  few  specimens 
from  the  English  Oolite  show 
almost  perfect  preservation  of 
the  original  creature  (see  Fig. 
143).  Ink-bags,  like  those  found 
in  modern  Squids,  are  some-  Fig.  142 

times   so   well    preserved   that  Internal  shell  of  a 


-B 


Belemnite,  re- 
stored. (From 
Norton's  "Ele- 
ments of  Geol- 
ogy," by  permis- 
sion of  Ginn  and 
Company,  Pub- 
lishers.) 


drawings  of  the  fossils  have 
actually  been  made  with  ink 
taken  from  their  own  ink-bags. 
Arthropods.  —  Among  the 
Crustaceans  the  familiar  Paleo- 
zoic Trilobites  and  Eurypterids 
were,  of  course,  gone,  and  forms 
much  higher  in  structure  had  become  abundant 
and  of  pretty  modern  aspect.  Thus,  among  Eu- 
crustaceans,  the  long-tailed  Decapods  (Macru- 
rans)  or  Lobster  forms  showed  many  genera  and 
species  (Fig.  144),  while  the  short-tailed  Deca- 
pods (Brachyura)  or  Crab  forms  made  their  first 
appearance,  though  they  were  not  numerous.  Many  types  inter- 
mediate between  the  long-tailed  and  short-tailed  Decapods  were 
very  common,  these  connecting  forms  being  of  special  evolutionary 


Fig.  143 

A  Jurassic  Bel- 
emnite, Belem- 
noteuthis  an- 
tiqui.  (Modi- 
fied after  Man- 
tell.) 


232 


HISTORICAL  GEOLOGY 


interest  because,  in  the  embryonic  development  of  the  modern 
Crab,  the  long  tail  of  the  early  stage  gradually  becomes  shorter 
and  practically  absent  in  the  adult  stage.  This  is  an  excellent 
example  of  the  so-called  "Law  of  Recapitulation"  (see  Fig.  145). 

Insects  were  numerous  in  cer- 
tain localities  at  least,  some  hun- 
dreds of  Jurassic  species  being 
known.  There  were  many  species 
of  the  simpler  forms,  includ- 
ing Grasshoppers.  Among  higher 
forms  the  Beetles  became  very 
abundant,  while  Flies  and  still 
higher  Insects  such  as  Bees,  Ants, 
and  Wasps  made  their  first  ap- 
pearance in  the  Jurassic.  Butter- 
flies, which  depend  upon  typical 
flowering  plants  (Angiosperms), 
were  not  certainly  present.  Proof 
of  their  presence  would  of  course 
show  the  existence  of  the  Angio- 
sperms in  the  Jurassic. 

Fishes.  —  Selachians  contin- 
ued to  be  common;  Dipnoans 
were  rare ;  and  Ganoids  were  still 
the  predominant  Fishes.  A  very 
important  change,  showing  pro- 
gress among  the  Fishes,  took 
place  by  the  first  appearance  of 
the  Teleosts  or  true  bony  Fishes, 
which  types  prevail  today.  The 
Jurassic  forms  were  simple,  not 
numerous,  and  they  were  fre- 


Fig.  144 

A  Jurassic  long-tailed  Decapod  (Ma- 
cruran).  (After  Neumayr's  "Erd- 
geschichte,"  from  Schuchert's 
"Historical  Geology,"  courtesy  of 
John  Wiley  and  Sons.) 


quently  on  the  border  between  true  Ganoids  and  true  Teleosts 
(Fig.  146). 

Amphibians.  —  Little  or  nothing  is  known  concerning  Jurassic 
Amphibians.  This  is  in  marked  contrast  with  their  prominent  de- 
velopment in  several  immediately  preceding  periods.  By  the  close  of 
the  Triassic  they  are  known  to  have  greatly  diminished,  never  again 
to  rise  to  prominence.  Only  a  few  small  forms,  such  as  Frogs,  Newts, 
and  Salamanders,  represent  this  once  great  class  at  the  present  time. 


THE  JURASSIC  PERIOD 


233 


Reptiles.  —  Viewed  in  the  broadest  way,  the  Reptiles  of  the 
Jurassic  were  much  like  those  of  the  Triassic,  except  that  they 


Fig.  145 

Three  stages  in  the  life  history  of  a  modern  Crab.  The 
larval  stage  B  is  very  similar  to  the  adult  Jurassic  form 
shown  in  figure  144.  (After  Couch,  from  Le  Conte's 
"Geology,"  permission  of  D.  Appleton  and  Company.) 

became  more  numerous  and  diversified.    By  some,  this  period  is 
regarded  as  the  culminating  time  of  the  Reptiles.     As  compared 


Fig.  146 

A  primitive  or  ancestral  Jurassic  Teleost,  Hypsocormus  insignis.     (From 
Scott's  "Geology,"  courtesy  of  The  Macmillan  Company.) 

with  the  Triassic  all  the  same  principal  groups  were  still  repre- 
sented, though  with  many  genera  and  species  changes.    The  more 


234 


HISTORICAL  GEOLOGY 


modern  forms,  such  as  Turtles,  greatly  increased,  but  Lizards  were 
still  very  subordinate.  Crocodiles  made  their  first  appearance. 
As  with  all  the  Mesozoic  periods,  the  principal  interest  surrounds 
the  great  groups  of  remarkable  extinct  Reptiles  such  as  Enalio- 
saurs,  Dinosaurs,  and  Pterosaurs.  It  will  be  more  convenient, 
however,  to  describe  Mesozoic  Reptiles  together  in  a  subsequent 
chapter. 

Birds.  —  A  very  important  feature  from  the  standpoint  of 
evolution  was  the  introduction  of  the  feathered  creatures  in  the 


Fig.  147 

The  earliest  known  Bird,  Archeopteryx  macrura,  from  the  Jurassic.  A, 
right  hand;  B,  right  foot;  C,  restoration  modified  after  Py craft. 
(From  Shimer's  "  Introduction  to  the  Study  of  Fossils,"  courtesy  of 
The  Macmillan  Company.) 

Jurassic.  "The  class  of  Birds  is  now  so  distinctly  separated  from 
all  others  and  the  connecting  links  obliterated,  that  the  earliest 
Birds  are  of  especial  interest  as  throwing  light  on  the  evolution  of 
this  class.  Until  1862  Birds  had  been  found  only  in  the  Tertiary, 
and  these  were  already  distinctly  differentiated  as  typical  Birds. 
But  in  that  year  there  was  found  in  the  Solenhofen  (Bavaria)  lime- 
stone, so  celebrated  for  its  marvelous  preservations  of  organisms, 
a  flying  feathered  biped,  and  therefore  presumably  a  Bird.  But 
how  different  from  our  usual  conceptions  of  this  class!  Along  with 


THE  JURASSIC  PERIOD  235 

its  distinctive  Bird-characters  of  feet,  limb-bones,  beak,  and  es- 
pecially of  feathered  wings,  it  had  the  long  tail  and  toothed  jaws 
(see  Fig.  147)  of  a  Reptile.  The  structure  of  the  tail  is  especially 
significant.  In  ordinary  Birds  the  tail  proper  is  shortened  up  to  a 
rudiment  and  ends  in  a  large  bone,  from  which  radiate  the  feathers 
of  the  tail-fan.  In  this  earliest  Bird,  on  the  contrary,  the  tail  proper 
is  as  long  as  all  the  rest  of  the  vertebral  column  put  together, 
consisting,  as  seen  in  the  figure,  of  twenty-one  joints  from  which  the 
fan  feathers  come  off  in  pairs  on  each  side.  The  tail-fan  of  this 
Bird  differs  from  that  of  typical  Birds  precisely  as  the  tail-fin  of 
the  earliest  Fishes  differs  from  that  of  typical  Fishes.  The  tail-fan 
of  this  earliest  Bird,  like  the  tail-fin  of  the  earliest  Fishes,  was 
vertebrated.  This  wonderful  reptilian  Bird  was  called  Archeop- 
teryx  ('primordial  winged  creature'),  and  the  species  macrura 
(' long-tailed').  ...  So  complete  is  the  mixture  of  the  two  kinds 
of  characters  that  some  zoologists  believe  that  the  reptilian  char- 
acters predominate,  and  that  it  should  be  called  a  Bird-like  Reptile. 
Most  agree,  however,  that  it  is  a  reptilian  Bird."  l  Thus,  while 
the  evidence  seems  conclusive  that  Birds  were  evolved  from  Rep- 
tiles, there  is  no  conclusive  evidence  that  they  were  derived  from 
the  flying  Reptiles  (Pterosaurs).  Rather  there  appears  to  have 
been  a  development  of  these  two  remarkable  groups  of  flying 
creatures  alongside  each  other. 

Mammals.  —  This  important  class,  first  known  from  the  Tri- 
assic,  continued  to  be  represented  by  only  comparatively  few 
small,  very  primitive  forms  in  the  Jurassic.  The  scant  records 
show  these  creatures  to  have  been  no  larger  than  Mice  or  Rats 
and  low  in  organization  (i.e.  Monotremes  or  Marsupials).  As 
already  stated,  Mammals  remained  very  subordinate  throughout 
the  Mesozoic  era. 

1  J.  LeConte:  Elements  of  Geology,  Ed.,  pp.  462-463. 


CHAPTER  XVI 
THE    CRETACEOUS    PERIOD 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

THE  term  Cretaceous,  from  the  Latin  " Greta"  for  chalk,  was 
given  to  the  period  because  of  the  prominence  of  chalk  beds  in 
the  rocks  of  this  age,  especially  in  England  and  France.  In  fact, 
one  of  the  most  striking  features  of  the  landscape  in  southern 
England  and  northern  France  consists  in  the  frequent  exposures 
of  beds  of  white  or  very  light  colored  chalk.  Perhaps  the  most 
famous  are  the  Dover  Cliffs  of  England.  In  many  parts  of  the 
world,  however,  the  Cretaceous  system  is  not  rich  in  chalk  deposits. 
In  the  United  States,  chalk  is  extensively  developed  in  the  Creta- 
ceous of  Alabama  and  Texas.  The  system  was  first  carefully 
studied  in  England,  but  the  names  of  the  French  subdivisions  are 
now  more  widely  employed. 

For  a  long  time  the  Cretaceous  system  has  been  known  to  be 
divisible  into  two  portions  —  a  Lower  and  an  Upper  —  often 
separable  by  unconformity,  and,  during  the  past  ten  or  twelve 
years,  some  authors  have  regarded  the  Lower  Cretaceous  as  a 
separate  system  called  "Comanchean"  from  a  locality  in  Texas. 
Recent  work  has,  however,  shown  that  the  Lower  and  Upper 
Cretaceous  are  not  so  sharply  and  widely  separated  as  was  formerly 
supposed,  particularly  in  the  type  region  of  Texas.  Hence  the  use 
of  "Comanchean"  as  a  distinct  system  and  period  name  seems 
inadvisable  at  the  present  time. 

Following  are  the  principal  subdivisions  of  the  Cretaceous 
as  now  recognized  in  Europe  and  North  America,  though  exact 
correlations  are  not  implied  (see  page  237). 

DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  Lower  Cretaceous.  The  surface  dis- 
tribution of  rocks  of  known  Lower  Cretaceous  age  is  shown  on 
the  accompanying  map  (Fig.  148).  With  the  exception  of  part  of 

236 


THE  CRETACEOUS  PERIOD 


237 


European 

North  Atlantic 
Coastal  Plain 

Alabama 

Texas 

Western 
Interior 

California 

(Danian. 

Manasquan. 
Rancocas. 

(Absent). 

Navarro. 

Laramie. 

Senonian. 

Monmouth. 
Matawan. 

Selma-Ripley. 

Taylor. 

Montana. 

Chico. 

"-    1  Turonian. 

Magothy. 

Eutaw. 
Tuscaloosa. 

Austin. 
Eagle  Ford. 
Woodbine. 

Colorado. 
Dakota. 

[  Cenomanian. 

Raritan. 

(unconformity) 

(unco  nformity) 

(unconformity) 

f  Albian. 

Patapsco. 

(Absent). 

Washita. 
Fredericks- 

Horsetown. 

g    |  Aptian. 

burg. 

^   "j  Barremian. 

Arundel. 

Lower 
Cretaceous. 

Trinity. 

Knoxville 

I  Neocomian. 

Patuxent. 

Kootenai. 
Morrison. 

(Probably) 
partly    Ju- 

rassic) . 

Virginia,1  these  rocks  are  seen  to  form  a  narrow  outcropping  belt 
at  the  western  margin  of  the  Atlantic  Coastal  Plain  from  New 
Jersey  to  Alabama.  Passing  eastward  from  the  exposed  belt,  well 
borings  show  that  much  at  least  of  the  whole  Coastal  Plain  is  under- 
lain with  Lower  Cretaceous  rocks.  "  The  sediments  (of  the  Coastal 
Plain)  in  general  form  a  series  of  thin  sheets  which  are  inclined 
seaward  (Fig.  155),  so  that  successively  later  formations  are  en- 
countered in  a  journey  from  the  inland  border  of  the  region 
toward  the  Coast"  (W.  B.  Clark). 

As  the  map  shows;  the  most  extensive  surface  distribution  of 
Lower  Cretaceous  rocks  is  in  Mexico  and  Texas.  Here,  too,  in 
passing  toward  the  (Gulf)  Coast  these  strata  are  known  to  be 
extensively  developed  under  cover  of  later  formations.  In  general, 
therefore,  the  actual  extent  of  Lower  Cretaceous  strata  in  the 
Atlantic  and  Gulf  Coastal  Plain  is  much  greater  than  the  surface 
exposures. 

Several  small  areas  are  known  in  the  western  United  States  in 
the  Rocky  Mountains  and  in  the  Coast  Range  of  northern  Cali- 
fornia. Large  surface  areas  occur  in  British  Columbia  and  Alaska. 
In  most  of  these  western  regions  the  Lower  Cretaceous  strata  are 
notably  folded  or  tilted,  so  that  their  full  extent  is  not  shown  by 
the  outcrops. 


1  In  this  part  of  Virginia  the  Lower  Cretaceous  strata  are  completely  con- 
cealed under  Tertiary  strata. 


238 


HISTORICAL  GEOLOGY 


Upper  Cretaceous.     As  seen  on  map  Fig.   149,  the  rocks  of 
Upper  Cretaceous  age  are  widely  exposed  at  the  surface  —  much 


Fig.  148 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Lower  Cretaceous 
strata  in  North  America.  (Modified  by  W.  J.  M.  after  Willis,  U.  S.  Geo- 
logical Survey.) 

more  so  than  those  of  Lower  Cretaceous  age.  In  the  eastern  and 
southern  United  States,  Upper  Cretaceous  strata  outcrop  as  com- 
paratively long,  narrow  belts  at  or  near  the  western  and  northern 


THE  CRETACEOUS  PERIOD 


239 


margin  of  the  Atlantic  and  Gulf  Coastal  Plain.    The  northernmost 
exposures  are  on  Martha's  Vineyard.    The  occasional  gaps  shown 


Fig.  149 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Upper  Cretaceous 
strata  in  North  America.  (Modified  by  W.  J.  M.  after  Willis,  U.  S.  Geo- 
logical Survey.) 

on  the  map  are  due  to  the  fact  that  the  Upper  Cretaceous  beds  are 
there  concealed  under  later  deposits.  From  the  outcropping  belts 
oceanward  or  gulfward,  the  Cretaceous  strata  dip  gently  under  the 


240  HISTORICAL  GEOLOGY 

later  (Cenozoic)  deposits  and  they  there  underlie  much,  if  not  all, 
of  the  Coastal  Plain  (Fig.  155). 

A  large  part  of  the  western  interior  shows  Upper  Cretaceous 
rocks  at  the  surface.  Because  of  the  usual  only  slightly  deformed 
character  of  the  strata  just  west  of  the  main  axis  of  the  Rocky 
Mountains,  there  is  a  large,  practically  solid  outcropping  area, 
while  within  the  Rockies,  where  much  deformation  has  affected 
the  rocks,  the  outcrops  are  much  more  patchy  in  distribution. 
Large  areas  of  Upper  Cretaceous  strata  are  also  concealed  under 
later  rocks  in  this  western  interior  region  (Fig.  149) . 

On  the  Pacific  Coast  and  in  Alaska  only  small  areas  of  Upper 
Cretaceous  strata  show  at  the  surface,  but  since  the  rocks  there 
are  usually  in  a  highly  deformed  condition,  they  are  really  con- 
siderably more  extensive  than  the  surface  exposures  seem  to 
indicate. 

Character  of  the  Rocks.  —  Atlantic  Coastal  Plain.  Three  well- 
known  Lower  Cretaceous  formations  (Patuxent,  Arundel,  and 
Patapsco)  of  the  Atlantic  Coast  have  long  been  called  the  Potomac 
series.  They  are  all  of  continental  origin.  Describing  these  forma- 
tions in  Maryland  and  Delaware,  W.  B.  Clark  says:  "The  Patux- 
ent formation  consists  mainly  of  sand,  generally  arkosic  and  in 
many  places  crossbedded,  with  small  masses  of  clay  scattered 
through  it.  The  formation  attains  a  thickness  of  350  feet.  It  has 
a  well-defined  early  Cretaceous  flora.  The  Arundel  formation 
consists  chiefly  of  clays,  which  in  places  carry  iron  ore  and  are 
commonly  lignitic.  It  has  a  thickness  of  about  125  feet.  It  is 
unconformable  to  the  Patuxent.  .  .  .  The  Patapsco  formation 
consists  of  highly  colored  and  variegated  clays  and  lighter  colored 
sandy  clays  and  sands.  It  has  a  thickness  of  200  feet  and  is  un- 
conformable to  the  Arundel."  l 

The  Upper  Cretaceous  deposits  rest  unconformably  upon  the 
Lower  Cretaceous.  According  to  Clark  the  Upper  Cretaceous 
formations  of  New  Jersey  are  typical  of  the  North  Atlantic  Coastal 
Plain  and  are  constituted  as  follows:  "The  Raritan  formation  .  .  . 
consists  of  clays,  sands,  and  gravels.  It  has  been  estimated  to 
have  a  maximum  thickness  of  about  300  feet  at  the  outcrop.  .  .  . 
The  Magothy  formation  unconformably  overlies  the  Raritan  forma- 
tion and  consists  of  dark  clays  and  light  sands.  The  clays  are 

1  W.  B.  Clark:  in  Index  to  The  Stratigraphy  of  North  America,  U.  S.  G.  S., 
Professional  Paper  71,  p.  610. 


THE  CRETACEOUS  PERIOD  241 

commonly  lignitic.  The  deposits  attain  a  maximum  thickness  of 
about  100  feet.  .  .  .  The  Matawan  consists  chiefly  of  dark-colored 
clays,  in  some  places  micaceous  and  glauconitic,  in  its  lower  part, 
and  of  sands,  with  an  interbedded  clayey  member,  locally  highly 
glauconitic,  in  its  upper  part.  It  attains  a  thickness  of  about  275 
feet,  although  a  thickness  of  400  feet  has  been  found  in  deep 
well  borings  east  of  its  outcrop.  It  lies  unconformably  on  the 
Magothy.  .  .  .  The  Monmouth  group  consists  of  sands  and  clays, 
with  an  interbedded  glauconitic  division  in  the  northern  part  of 
the  area.  Toward  the  south  the  upper  sandy  formation  disappears. 
The  greatest  thickness  of  the  group  is  about  150  feet.  The  Mon- 
mouth is  conformable  to  the  Matawan.  .  .  .  The  Rancocas  consists 
largely  of  greensand  marls  and  sandy  calcareous  beds  which  have 
a  maximum  thickness  in  southern  New  Jersey  of  about  125  feet. 
It  is  conformable  to  the  Monmouth.  .  .  .  The  Manasquan  forma- 
tion consists  of  greensand  marls  and  attains  a  thickness  of  about 
50  feet.  It  is  conformable  to  the  Rancocas."  l 

Alabama.  Lower  Cretaceous  strata  (unnamed)  of  Alabama, 
according  to  Stephenson,  consist  of  "irregular  bedded,  coarse, 
arkosic,  more  or  less  micaceous  sand,  with  subordinate  lenses  of 
usually  massive  clay  of  greater  or  lesser  purity.  The  terrane  rests 
upon  a  basement  of  crystalline  rocks  and  is  separated  from  the 
overlying  Eutaw  and  other  Upper  Cretaceous  and  Tertiary  forma- 
tions by  an  unconformity."  2 

According  to  Stephenson  "the  Tuscaloosa  formation  consists 
of  irregularly  bedded  sands,  clays,  and  gravels  having  an  estimated 
total  thickness  of  1000  feet.  .  .  .  The  Eutaw  formation  consists 
predominantly  of  more  or  less  glauconitic  sand,  massive  to  cross- 
bedded  in  structure,  with,  in  parts  of  the  terrane,  irregularly 
interbedded  fine  laminae  and  laminated  layers  of  dark  clay.  .  .  . 
The  total  thickness  of  the  formation  is  estimated  to  be  from  400 
to  500  feet.  .  .  .  The  £elma  chalk  consists  in  the  main  of  more 
or  less  argillaceous  and  sandy  limestones  rendered  chalky  by  their 
large  content  of  Foraminiferal  remains,  with  interbedded  layers  of 
nearly  pure,  hard  limestone  at  wide  intervals.  In  western  Ala- 
bama the  terrane  has  a  measured  thickness  of  930  feet.  .  .  .  The 
typical  beds  of  the  Ripley  formation  consist  of  more  or  less  calcare- 
ous and  glauconitic  sands,  sandy  clays,  impure  limestones,  and 

1  W.  B.  Clark:  U.  S.  G.  S.,  Professional  Paper  71,  pp.  609-610. 

2  L.  W.  Stephenson:  U.  S.  G.  S.,  Professional  Paper  81,  p.  20. 


242  HISTORICAL  GEOLOGY 

marls,  of  marine  origin,  reaching  an  estimated  thickness  in  this 
region  of  250  to  350  feet."  1 

From  the  above  descriptions,  the  Atlantic  and  eastern  Gulf 
Coastal  Plain  Cretaceous  deposits  are  seen  to  be  largely  uncon- 
solidated  and  only  slightly  tilted  sediments. 

Texas.  In  the  Texas  region  the  Trinity  formation  consists 
mostly  of  light  colored  sands,  with  some  alternating  marls,  clays, 
and  limestones.  Its  lower  portion  is  of  continental  origin,  while 
its  upper  portion  is  marine.  The  whole  formation  attains  a  maxi- 
mum thickness  of  about  2000  feet.  The  Fredericksburg  formation 
is  typically  almost  entirely  chalky  limestone  of  marine  origin  from 
1000  to  5000  feet  thick.  It  covers  wide  areas  in  Mexico  and  Texas. 
The  Washita  formation  2  comprises  chiefly  alternations  of  light  and 
dark  colored  marly  clays,  limestones,  and  sandy  limestones  whose 
thickness  is  from  200  to  400  feet.  This  formation  extends  across 
much  of  Mexico,  Texas,  and  northward  into  Oklahoma,  southeast- 
ern Kansas,  eastern  Colorado,  and  possibly  into  Wyoming. 

The  Woodbine  formation,  according  to  Hill,3  is  made  up  of 
ferruginous  sands  and  clays  (600  i  feet  thick) ;  the  Eagle  Ford 
formation  is  essentially  bituminous  clay  with  some  limestone 
(600  i  feet  thick) ;  the  Austin  formation  is  largely  impure  chalk 
with  some  softer  beds  of  marl  (600  it  feet  thick) ;  the  Taylor  for- 
mation is  calcareous  clay  marl  (several  hundred  feet  thick);  and 
the  Navarro  formation  is  mostly  made  up  of  sands,  chalks,  and 
clays  with  some  glauconite  (thickness?). 

Western  Interior.  In  the  western  interior  region  mostly  just 
east  of  the  main  axis  of  the  Rocky  Mountains  from  Colorado 
northward,  there  occur  certain  formations  —  Morrison,  Kootenai, 
etc.  —  of  rather  doubtful  age  and  origin.  They  consist  mostly  of 
shales,  sandstones,  and  limestones,  and,  in  part  at  least,  they  are 
Lower  Cretaceous  deposits  of  continental  origin. 

The  Dakota  formation  is  chiefly  sandstone,  mostly  of  marine 
origin,  and  up  to  100  feet  thick.  The  Colorado  formation  is  very 
largely  of  marine  origin  and  comprises  mostly  clastic  sediments 
but  with  considerable  chalk.  The  Montana  formation  comprises 
mostly  clastic  sediments  of  marine  origin,  though  with  some 
continental  deposits,  as,  for  example,  local  coal  beds.  It  shows  a 

1  L.  W.  Stephenson,  U.  S.  G.  S.,  Professional  Paper  81,  pp.  20-21. 

2  Recent  work  has  shown  the  Washita  to  be  partly  Upper  Cretaceous. 

3  U.  S.  G.  S.,  Professional  Paper  71,  pp.  20-21. 


THE  CRETACEOUS  PERIOD  243 

remarkable  variation  in  thickness  of  from  8700  feet  in  Colorado 
to  only  200  feet  in  the  Black  Hills  of  South  Dakota.  The  Laramie 
formation  is  quite  certainly  mostly  of  non-marine  origin,  with 
fresh-water  and  land  deposits  (including  much  coal)  common. 
The  formation  shows  a  variable  thickness  possibly  up  to  several 
thousand  feet,  and  it  occurs  only  in  the  western  interior  region. 

Pacific  Coast.  —  On  the  Pacific  Coast,  the  Lower  Cretaceous 
is  remarkably  developed,  where  it  shows  a  maximum  thickness. 
According  to  Diller,  the  older  or  Knoxville  l  series,  comprising 
nearly  20,000  feet  of  shales  with  some  interbedded  sandstones 
and  limestones,  is  overlain  conformably  by  the  Horsetown  series 
of  sandstones  and  shales  about  6000  feet  thick.  This  enormous 
thickness  of  sediments  is  clearly  of  shallow-water  origin,  the  rocks 
now  nearly  always  being  distinctly  folded  or  tilted.  In  southern 
California,  too,  the  system  is  pretty  thick  and  there  contains  some 
volcanic  rocks.  Lower  Cretaceous  strata,  usually  folded  and  some- 
times metamorphosed,  also  are  widely  developed  in  British  Colum- 
bia and  Alaska  with  some  coal  in  both  regions  and  some  volcanic 
rock  in  the  former. 

The  Upper  Cretaceous  on  the  Pacific  Coast  is  represented  by 
the  single  great  Chico  formation,  but  both  the  oldest  and  the  young- 
est portions  of  the  series  are  often  not  represented  at  all.  The 
Chico  is  a  marine  deposit  from  a  few  hundred  to  several  thousand 
feet  thick.  It  is  prominently  developed  in  the  Coast  Range 
Mountains  from  Lower  California  to  British  Columbia.  It  consists 
mostly  of  sandstones,  shales,  and  conglomerates,  and  is,  in  some 
places,  conformable,  and  in  others  unconformable,  upon  the  Lower 
Cretaceous. 

Thickness  of  the  Cretaceous.  —  The  sj^stem  shows  a  maxi- 
mum thickness  of  fully  1700  feet  on  the  north  Atlantic  Coast; 
3000+  feet  in  the  eastern  Gulf  region;  3500  to  7500  feet  in  the 
western  Gulf  region;  10,000  to  15,000  feet  in  the  western  interior 
region,  though  usually  much  less  in  any  one  locality;  and  26,000 
feet  on  the  Pacific  Coast. 

Igneous  Rocks.  —  Volcanic  rocks  in  the  Lower  Cretaceous  are 
known  only  in  British  Columbia  and  in  the  Coast  Range  of  south- 
ern California.  Igneous  rocks  (chiefly  lavas)  of  late  Cretaceous 
and  Tertiary  ages  occur  in  vast  quantities  over  great  areas  in 

1  According  to  some  workers  the  Knoxville  is  now  regarded  as  partly  Ju- 
rassic in  age. 


244  HISTORICAL  GEOLOGY 

central  western  North  America.    The  igneous  activity  represented 
by  these  rocks  is  more  fully  described  in  succeeding  pages. 

PHYSICAL  HISTORY 

Atlantic  and  Eastern  Gulf  Coasts.  —  The  Cretaceous  period 
opened  with  the  coast  line  of  the  eastern  United  States  somewhat 
farther  out  than  it  now  is,  but,  early  in  the  period,  there  was  enough 
subsidence,  or  possibly  warping,  of  the  coastal  lands  to  allow 
deposition  of  sediments  over  much  of  what  is  now  known  as  the 
Atlantic  and  eastern  Gulf  Coastal  Plain.  That  but  little  down- 
warping  of  the  surface  was  necessary  in  order  to  produce  proper 
conditions  for  this  sedimentation  is  evident,  because  the  coastal 
lands  just  prior  to  the  Cretaceous  were  already  low-lying  as  a  result 
of  the  long  Jurassic  erosion  interval.  There  was  just  enough 
warping  of  the  low  coastal  lands  to  produce  wide  flats,  flood-plains, 
shallow  lakes,  and  marshes  back  from  the  real  coast  line.  Over 
such  areas  were  deposited  the  sediments  derived  from  the  Pied- 
mont Plateau  and  Appalachian  areas.  The  very  irregular  arrange- 
ment of  the  deposits  (Potomac)  and  their  rich  content  of  fossil 
land  plants  afford  conclusive  evidence  that  the  sediments  were 
accumulated  under  continental  conditions. 

The  pretty  widespread  unconformity  between  the  Lower  and 
Upper  Cretaceous  in  these  regions  proves  that,  about  the  close  of 
the  Lower  Cretaceous,  there  must  have  been  enough  emergence  of 
the  lands  to  convert  the  basins  of  deposition  into  areas  of  erosion. 
Early  in  the  Upper  Cretaceous,  however,  a  submergence  of  the 
coastal  lands  took  place,  inaugurating  the  deposition  of  the  Upper 
Cretaceous  strata.  The  general  character,  mostly  marine  1  origin, 
and  present  extent  of  these  deposits  prove  that  the  submergence 
allowed  a  shallow  sea  to  spread  over  much  of  what  is  now  called 
the  Atlantic  and  eastern  Gulf  Coastal  Plain.2  In  this  connection  it 
is  very  important  to  note  that  Appalachia,  the  great  land-mass 
which  had  persisted  through  the  many  millions  of  years  of  the 
Paleozoic  era  as  well  as  most  of  the  Mesozoic  era,  disappeared 
under  the  Cretaceous  sea  not  again  to  reappear. 

Texas.  —  Early  in  Trinity  time  continental  deposits  (sands) 
only  were  forming  over  the  Texas  region,  but  later  in  the  epoch 

1  Some  beds  of  continental  origin  occur  in  the  Upper  Cretaceous  of 
Maryland  and  New  Jersey. 

2  Certain  minor  oscillations  of  level  are  here  disregarded. 


THE  CRETACEOUS  PERIOD 


245 


LOWER  CRETACEOUS  r 

NORTH    AMERICA 


LEGEND 

OCEANIC  BASINS 

MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA,  MORE  LIKELY  LAND 
LANDS 
INDETERMINATE  AREAS 


CONTINENTAL  DEPOSITS,  SOMETIMES 
INCLUDING  MARINE  SEDIMENTS 


Fig.  150 

Paleogeographic   map   of   North  America  during  Lower  Cretaceous    time. 
(Slightly  modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.) 


246  HISTORICAL  GEOLOGY 

marine  waters  spread  over  the  region.  During  all  of  Fredericks- 
burg  time  a  clear  and  unusually  deep  epicontinental  sea"  occupied 
much  of  Mexico  and  Texas  and  immediately  adjoining  regions. 
Great  chalk  deposits  were  formed  in  this  clear  sea.  Perhaps  the 
maximum  northward  extension  of  the  Lower  Cretaceous  sea  took 
place  during  Washita  time,  when  marine  waters  probably  reached 
as  far  northward  as  Colorado  (see  map  Fig.  150). 

Throughout  Upper  Cretaceous  time,  from  Woodbine  to  Na- 
varro  inclusive,  marine  waters  appear  to  have  persisted  over  the 
Texas  area,  having  been  particularly  clear  during  the  deposition 
of  the  Austin  chalk. 

Western  Interior  Region.  —  The  physical  history  of  this  area 
during  Lower  Cretaceous  time  is  still  somewhat  problematical, 
but  the  best  evidence  seems  to  show  that,  just  east  of  the  site  of 
the  Rockies,  deposits  of  continental  origin  (Morrison  and  Kootenai) 
were  forming  very  much  like  those  of  the  Potomac  on  the  Atlantic 
Coast. 

Pretty  early  in  the  Upper  Cretaceous,  the  western  interior 
region  witnessed  a  very  extensive  marine  transgression  beginning 
during  Dakota  time  and  probably  reaching  a  maximum  during 
Colorado  time.  In  the  comparatively  clear  waters  of  this  Colorado 
sea  were  accumulated  the  chalk  and  other  marine  deposits.  This 
great  marine  invasion  must  take  rank  as  one  of  the  most  extensive 
in  the  history  of  the  continent,  the  marine  waters  having  spread 
from  the  Gulf  of  Mexico  northward  over  the  western  interior 
region  to  the  Arctic  Ocean  by  way  of  what  is  now  the  Mackenzie 
River  Valley  (see  map  Fig.  151).  There  is  no  good  evidence  that 
this  vast  western  interior  sea  had  direct  connection  with  the  Pacific 
Ocean.  In  the  latter  portion  of  the  period  (Laramie)  marine 
waters  did  not  prevail  over  the  immediate  Rocky  Mountain  dis- 
trict through  the  United  States  and  Alberta.  Sufficient  emergence 
"  formed  a  coastal  plain,  extensive  marshes  prevailed,  and  the 
marsh  deposits  became  coal  beds.  Sea,  marshes,  and  river  plains 
alternated  in  sequence  till  near  the  close  of  the  Cretaceous  period" 
(Bailey  Willis). 

Pacific  Coast.  —  Rather  remarkable  physical  conditions  must 
have  obtained  in  California,  especially  in  the  north,  to  give  rise  to 
such  a  phenomenal  thickness  of  sediments  during  this  one  period. 
Apparently  the  explanation  is  not  far  to  seek,  because  the  newly 
upraised  Sierras  must  have  undergone  vigorous  erosion  with  rapid 


THE  CRETACEOUS  PERIOD 


247 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONT1NENTAL 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAND 
LAN 
INDETERMINATE  AREAS 

POLAR 


Fig.  151 

Paleogeographic   map   of   North   America   during   Upper   Cretaceous   time. 
(Slightly  modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.) 


248 


HISTORICAL  GEOLOGY 


accumulation  of  materials  in  the  marine  waters  which  then  occu- 
pied the  sites  of  the  present  Great  Valley  and  Coast  Range  of 
California.  According  to  Bailey  Willis,  "a  bold  peninsula  devel- 
oped from  Oregon  south  to  Santa  Barbara  (California)"  during 
Lower  Cretaceous  time,  as  shown  on  the  map  Fig.  150,  but  accord- 
ing to  certain  others  marine  waters  spread  over  most  of  the  Coast 
Range  district  during  both  Lower  and  Upper  Cretaceous  times. 


Fig.  152 

Typical  exposure  of  Upper  Cretaceous  (Selma)  chalk  in  Alabama. 
L.  W.  Stephenson,  U.  S.  Geological  Survey,  Prof.  Paper  81.) 


(After 


In  British  Columbia  and  Alaska  the  presence  of  marine  strata 
proves  the  existence  of  sea  water  over  the  areas  indicated  on  the 
accompanying  maps,  though  the  coal  beds  show  that  great  swamps 
or  lagoons  must  have  existed  locally. 

Close  of  the  Period  in  the  West  (Rocky  Mountain  Revolu- 
tion). —  The  close  of  the  Cretaceous  period,  or,  what  is  the  same 
thing,  the  close  of  the  Mesozoic  era,  was  marked  by  one  of  the  most 
profound  and  widespread  physical  disturbances  in  the  history  of 


THE  CRETACEOUS  PERIOD 


249 


North  America  since  pre-Cam- 
brian  time.  Over  the  Rocky 
Mountain  district  there  had 
been  more  or  less  deposition  of 
sediments  (both  marine  and 
continental)  throughout  Pale- 
ozoic and  Mesozoic  times. 
Toward  the  close  of  the  Cre- 
taceous, there  was  vigorous 
deformation,  including  both 
folding  and  dislocations  of  the 
strata,  not  only  throughout  the 
Rocky  Mountain  district  in 
North/America  fr;6m  the  Arctic 

a,  but 
.f  the 
Horn 
one- 
d  the 
il  dis- 
ci the 


Ocean*  to  Central  Ameri 
also  elven  along  the  line 
Andes  Mountains  to  Cap 
—  altogether  more  tha: 
fourth,  of  the |  way  arou 
earth.  '  This  £reat  crust 
turban^e  hasj  been  call 
"RockW  Mountain  ReVolu- 
tion."  I  While-  the  folding  was 
usually  foot  nearly  as  intense  as 
at  the  time  ofl  the  "  Appalach- 
ian Revolution,"  nevertheless 
there  w$re  v4ry  considerable 
uplifts  accompanied  by  moder- 
ate folding  <Jf  the  strata  in 
many  parts  of  the  district  (Fig. 
154).  That/  portion  of  the 
Rockies  north  of  the  United 
States  (so-called  Laramide 
Range)  suffered  the  severest 
deformation  where  strata  esti- 
mated at  40,000  to  50,000  feet 
thick  were  folded  and  faulted 
into  a  range  which  was  prob- 
ably no  less  than  20,000  feet 
high.  The  Rocky  Mountains 


250  HISTORICAL  GEOLOGY 

may  be  truly  said  to  have  had  their  beginning  at  that  time,  al- 
though their  existing  altitude  and  relief  features  are  largely  due 
to  later  movements  and  erosion.  Instead  of  folds,  great  thrust 
faults  were  sometimes  developed,  a  fine  example  being  near  the 
Canadian  boundary,  where  Algonkian  rocks  were  pushed  about 
7  miles  over  Cretaceous  rocks.1 

Another  very  important  physical  disturbance,  accompanying 
the  " Rocky  Mountain  Revolution"  in  the  northwestern  United 
States  and  southern  British  Columbia,  was  the  inauguration  of 
vast  igneous  (chiefly  volcanic)  activity,  which  continued  almost 
unabated  through  the  immediately  succeeding  Tertiary  period. 


Fig.  154 

Structure  section  in  the  Rocky  Mountains  of  western  Montana  showing  moder- 
ate folding  of  Cretaceous  and  older  rocks.  Argn,  Archean;  Cg,  Cf,  Cam- 
brian; Dt,  Dj,  Devonian;  Cq,  Cn,  Carboniferous;  Kl,  Kmc,  Kd,  Cretaceous. 
(After  Peale,  U.  S.  Geological  Survey,  Folio  24.) 

Volcanic  and  fissure  eruptions  took  place  on  a  grand  scale,  and 
lava-flows  accumulated  to  a  thickness  of  several  thousand  feet 
over  an  area  of  about  200,000  square  miles.  This  was  the  time 
of  greatest  igneous  activity  in  North  America  since  pre-Cambrian 
days. 

Close  of  the  Period  in  the  East.  The  Cretaceous  Peneplain 
and  its  Uplift,  —  Turning  our  attention  to  the  eastern  part  of  the 
continent,  we  find  that  significant  changes  took  place  there  also. 
In  fact  the  area  of  the  eastern  United  States  was  subjected  to  the 
greatest  crustal  disturbance  since  the  " Appalachian  Revolution" 
toward  the  close  of  the  Paleozoic. 

During  all  of  the  Mesozoic  era  most  of  the  eastern  portion  of 
the  United  States,  except  the  Coastal  Plains  during  part  of  the 
time,  was  above  sea  water  and  undergoing  erosion,  so  that,  as  a 
result  of  this  very  long  time  of  wear,  the  region  was  reduced  to  the 
condition  of  a  more  or  less  perfect  peneplain.  It  is  known  as  the 

1  It  is  possible  that  this  fault  was  developed  a  little  later,  that  is  in  early 
or  middle  Tertiary  time. 


THE  CRETACEOUS  PERIOD  251 

" Cretaceous  Peneplain/'  because  of  its  best  development  during 
the  Cretaceous  period  (Fig.  155).  This  vast  plain  extended  over 
the  areas  of  the  Appalachian  Mountains,  Piedmont  Plateau,  all 
of  New  York  state,  the  Berkshire  Hills,  and  the  Green  and  White 
Mountains.  Its  most  perfect  development  was  in  the  northern 
Appalachians  as,  for  example,  from  east-central  Pennsylvania  to 
Virginia,  where  hard  and  soft  rocks  alike  had  been  so  thoroughly 


Fig.  155 

Diagrammatic  section  through  the  Atlantic  slope  at  about  the  latitude  of 
northern  New  Jersey,  showing  the  structures  and  relations  of  the  various 
physiographic  provinces  as  they  now  exist. 

A  to  B,  folded  Paleozoic  strata  of  the  Appalachian  Mountains,  with  hard 
strata  standing  out  to  form  the  ridges;  B  to  C,  Piedmont  Plateau,  con- 
sisting of  highly  folded  and  metamorphosed  rocks  of  pre-Cambrian  and 
early  Paleozoic  ages;  C  to  E,  Triassic  strata,  showing  tilting  and  faulting  of 
the  beds  and  mode  of  occurrence  of  a  sheet  of  igneous  rock  (D)  which 
outcrops  to  form  low  ridges;  E  to  H,  Coastal  Plain,  consisting  of  com- 
paratively thin  sheets  of  unconsolidated  sediments;  E  to  F,  Cretaceous 
beds;  F  to  G,  Tertiary  beds;  G  to  H,  Quaternary  beds;  H,  present  coast 
line. 

The  dotted  line  represents  the  peneplain  character  of  the  surface,  except  for 
the  tilting,  toward  the  close  of  the  Mesozoic  era.  (After  W.  J.  Miller,  N.Y. 
State  Mus.  Bui.  168.) 

cut  down  that  no  masses  projected  notably  above  the  level  of  the 
low-lying  plain. 

Farther  northward,  however,  over  New  York  and  western 
New  England,  its  development  was  less  perfect,  so  that  certain 
masses  of  harder  rock  stood  out  more  or  less  prominently  above 
the  general  level  of  the  plain. 

As  Berkey  says:  "The  continent  stood  much  lower  than  now. 
Portions  that  are  now  mountain  tops  and  the  crests  of  ridges 
were  then  constituent  parts  of  the  rock  floor  of  the  pene- 
plain not  much  above  sea  level.  .  .  .  The  ridges  and  valleys,  the 
hills,  mountains,  and  gorges  of  the  present  were  not  in  existence, 


252  HISTORICAL  GEOLOGY 

except  potentially  in  the  hidden  differences  of  hardness  or  rock 
structure.    Such  conditions  prevailed  over  a  very  large  region  — 
certainly  all  of  the  eastern  portion  of  the  United  States."  l 

The  Cretaceous  period  was  closed  in  eastern  North  America  by 
a  disturbance  which  produced  an  upwarp  of  this  vast  Cretaceous 
peneplain  with  maximum  uplift  of  from  2000  to  3000  feet,  follow- 
ing the  general  trend  of  the  Appalachians  and  thence  through 
northern  New  York  and  western  New  England.  This  upward 
movement  was  unaccompanied  by  any  renewed  intense  folding  of 
the  strata,  the  effect  having  been  to  produce  a  broad  dome  sloping 
eastward  and  westward,  and  northward  to  the  Gulf  of  St.  Lawrence 
and  southward  to  the  Gulf  of  Mexico.  The  upward  movement 
was,  however,  accompanied  by  the  retreat  of  the  sea  from  the 
Coastal  Plain  area,  which  thus  accounts  for  the  widespread  uncon- 
formity there  between  the  Cretaceous  and  the  overlying  Tertiary 
strata. 

Another  prominent  effect  of  this  great  uplift  was  to  revive  the 
activity  of  the  streams  so  that  they  once  more  became  active 
agents  of  erosion,  and  the  present  major  topographic  features  of 
the  eastern  United  States  have  been  largely  produced  by  the 
erosion  and  dissection  of  this  upraised  Cretaceous  peneplain. 
Where  the  peneplain  was  best  developed,  the  typical  Appalachian 
ridges  and  valleys,  running  parallel  to  the  trend  of  the  mountain 
range,  are  now  beautifully  shown.  These  valleys  are  the  trenches 
of  the  upraised  peneplain,  while  the  ridges  have  developed  along 
the  belts  of  hard  rock,  their  summits  actually  representing  portions 
of  the  old  peneplain  surface  (Fig.  155).  These  ridges  all  rise  to 
the  same  general  level  for  miles  around,  and  as  viewed  from  the 
summit  of  any  one  of  them,  the  concordant  altitudes  give  rise  to 
what  is  called  the  "even  sky-line,"  which  is  a  most  striking  feature 
of  the  landscape.  In  New  York  state  and  western  New  England 
remnants  of  the  upraised  peneplain  surface  are  also  distinctly 
shown. 

FOREIGN  CRETACEOUS 

Europe.  —  Toward  the  close  of  the  Jurassic  and  about  the 

beginning  of  the  Cretaceous,  continental  deposits  were  forming 

in  parts  of  central  and  western  Europe.    Often  these  deposits 

grade  from  the  Jurassic  into  the  earliest  Cretaceous.    The  Alpine 

1  C.  P.  Berkey:  N.  Y.  State  Mus.  Bull.  146,  p.  67. 


THE  CRETACEOUS  PERIOD 


253 


region  continued  to  be  submerged  under  sea  water.  Soon  after 
the  beginning  of  the  Cretaceous,  a  more  or  less  interrupted 
marine  transgression  caused  considerable  areas  of  western  and 
central  Europe  to  become  submerged,  the  deposits  including  both 
marine  and  non-marine  beds.  At  the  same  time  marine  waters 
were  more  extended  over  the  southern  part  of  the  continent.  Map 


Fig.  156 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  during 
Lower  Cretaceous  time.     (Slightly  modified  after  De  Lapparent.) 

Fig.  156  affords  a  general  picture  of  the  relations  of  land  and  water 
at  that  time.  In  western  and  central  Europe  all  types  of  common 
sedimentary  rocks  were  formed,  as  well  as  some  beds  of  coal  in 
Germany.  As  would  be  expected,  because  of  the  more  prevalent 
marine  conditions  in  southern  Europe,  limestone  was  more  com- 
monly formed  there.  The  conditions  just  described  continued 
essentially  till  the  close  of  the  Lower  Cretaceous,  when  only  com- 
paratively slight  sea  retrogressions  took  place,  as  proved  by  the 
fact  that  the  Upper  Cretaceous  rocks  usually  rest  conformably 


254 


HISTORICAL  GEOLOGY 


upon  the  Lower  Cretaceous.  Thus  in  Europe  there  is  not  such  a 
sharp  break  between  the  Lower  and  Upper  Cretaceous  as  in  North 
America. 

As  in  North  America,  so  in  Europe,  Upper  Cretaceous  time 
was  marked  by  a  great  transgression  of  the  sea.  This  marine 
invasion,  which  started  in  the  Lower  Cretaceous,  continued  with 


Fig.  157 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  during 
early  Upper  Cretaceous  time.  (Slightly  modified  after  De  Lap- 
parent.) 

only  slight  interruptions  well  into  the  Upper  Cretaceous,  when 
much  of  Europe,  except  Scandinavia  and  Russia,  was  submerged, 
as  shown  by  map  Fig.  157.  As  in  the  Lower  Cretaceous,  the  most 
common  rock  to  form  in  southern  Europe  was  limestone.  In 
central-western  Europe  all  types  of  ordinary  sediments  are  repre- 
sented, but,  as  already  stated,  in  northern  France  and  southern 
England,  the  Cretaceous  contains  much  chalk  (e.g.  Dover  Cliffs) 
which  is  made  up  of  Foraminiferal  shells  and  which  implies  clear, 


THE  CRETACEOUS  PERIOD  255 

if  not  fairly  deep,  sea  water  for  its  accumulation.  Considerable 
greensand  also  occurs  in  the  European  Upper  Cretaceous. 

Toward  the  close  of  the  period  (Danian  time)  there  were  up- 
ward movements  sufficient  to  increase  the  land  areas  and  establish 
basins  of  non-marine  sedimentation  from  Spain  to  and  across  the 
Alpine  region  as  shown  by  the  Cretaceous  fresh-water  deposits 
there. 

Other  Continents.  —  Rather  extensive  areas  of  Cretaceous 
occur  in  New  Zealand  and  Australia,  where  the  rocks  are  frequently 
coal  bearing  and  an  unconformity  often  separates  the  Lower  and 
Upper  portions  of  the  system. 

Southwestern  Asia,  India  (in  the  Himalayas),  China,  Japan, 
and  Siberia  all  show  more  or  less  extensive  development  of  Cre- 
taceous strata.  Over  northern  Africa  extensive  areas  of  marine 
Cretaceous  rocks  show  much  of  that  region  to  have  been  sub- 
merged during  the  period.  In  South  Africa  Cretaceous  rocks 
(especially  the  Lower)  are  considerably  developed.  A  feature  of 
special  importance  in  India  was  the  inauguration,  late  in  the  period, 
of  one  of  the  greatest  times  of  vulcanism  since  the  pre-Cambrian 
and  quite  comparable  to  that  of  western  North  America  already 
referred  to.  This  is  known  as  the  Deccan  lava  region  where  some 
200,000  square  miles  are  covered  by  lava  flows  whose  aggregate 
thickness  reaches  several  thousand  feet. 

In  South  America  Cretaceous  rocks  are  widely  distributed, 
especially  in  Brazil,  where  a  notable  marine  invasion  occurred  in 
the  Upper  Cretaceous,  though  in  places  only  continental  deposits 
were  formed.  East  of  the  Andes  the  Lower  Cretaceous  rocks  are 
mostly  non-marine.  High  in  the  eastern  Andes  and  in  southern 
Patagonia  marine  Upper  Cretaceous  strata  are  known.  Toward 
the  close  of  the  period  came  the  great  orogenic  disturbance,  accom- 
panied by  much  volcanic  activity,  in  the  Andes  Mountains  district. 

CLIMATE 

As  would  be  expected  because  of  the  unusually  extensive 
epicontinental  seas,  the  climate  of  the  period  seems  to  have  been 
mild  to  warm  and  pretty  uniform  but  with  some  distinction  of 
climatic  zones.  The  fossil  evidence  (e.g.  plants  in  the  Cretaceous 
of  Greenland)  indicates  mildness  of  climate  even  within  the  Arctic 
circle. 


256  HISTORICAL  GEOLOGY 

ECONOMIC  PRODUCTS 

Coal  beds  of  moderate  extent  and  value  are  known  in  the 
Lower  Cretaceous  rocks  of  Alaska,  British  Columbia,  Australia, 
and  Germany. 

Coal  is  extensively  developed  in  the  later  Cretaceous  of  the 
western  interior  region  of  the  United  States.  It  is  estimated  that 
fully  100,000  square  miles  are  underlain  with  chiefly  lignitic  and 
bituminous  coals  as  well  as  a  little  anthracite  coal.  Considerable 
Cretaceous  coal  also  occurs  in  Australia  and  New  Zealand. 

The  greensands  (glauconitic)  of  the  Atlantic  Coastal  Plain, 
especially  in  New  Jersey  and  Virginia,  were  formerly  extensively 
used  as  land  fertilizers  on  account  of  their  phosphoric  acid  content. 

A  heavy  production  of  petroleum  has  been  obtained  from  the 
Cretaceous  strata  of  Texas,  particularly  in  the  vicinity  of  Beau- 
mont. Both  oil  and  gas  are  obtained  from  the  Cretaceous  in 
Louisiana  and  Wyoming. 

Cretaceous  limestones  are  quarried  in  Kansas,  Nebraska,  and 
Iowa  for  building  stone. 

The  most  important  sulphur  deposits  in  the  United  States  occur 
in  rocks  of  Cretaceous  age  in  Louisiana. 

The  vast  supply  of  underground  water  obtained  from  the  Cre- 
taceous (Dakota)  sandstone  in  the  Great  Plains  region  is  worthy 
of  special  mention.  Much  artesian  water  is  also  derived  from 
Cretaceous  beds  in  the  Atlantic  and  Gulf  Coastal  Plain.  In  the 
regions  just  mentioned  the  water  is  held  under  pressure  in  porous 
sandstone  by  overlying  impervious  clay  or  shale. 

LIFE  OF  THE  CRETACEOUS 

.  Plants.  —  Early  in  the  period  the  plants  were  very  much  like 
those  of  the  preceding  Mesozoic  periods,  the  dominant  types  still 
having  been  Ferns,  Equisetce,  Cycads,  and  Conifers. 

Among  the  Gymnosperms,  which  were  distinctly  subordinate 
and  a  good  deal  like  those  of  the  present  day,  a  feature  of  special 
interest  was  a  considerable  development  of  the  genus  Sequoia 
which  is  still  represented  by  the  so-called  "Big  Trees"  and  giant 
Redwoods  of  California. 

Before  the  Cretaceous,  Angiosperms  are  not  definitely  known 
to  have  existed,  but  in  North  America  there  can  be  no  possible 


THE  CRETACEOUS  PERIOD 


257 


doubt  of  their  presence  —  both  Monocotyledons  and  Dicotyle- 
dons —  even  in  late  Lower  Cretaceous  time.  By  the  close  of  the 
period  the  Angiosperms  had  developed  so  phenomenally  as  to 
attain  a  position  of 
supremacy  among 
plants,  which  position 
they  have  maintained 
ever  since.  This  com- 
paratively sudden  ap- 
pearance and  remark- 
able development  of 
the  Angiosperms  "was 
one  of  the  most  im- 
portant and  far-reach- 


Fig.  158 

Cretaceous  Foraminifers,  greatly  enlarged.  (Af- 
ter Calvin,  from  Le  Conte's  "Geology,"  per- 
mission of  D.  Appleton  and  Company.) 


ing  biologic  events  the 

world  has  known.  .  .  . 

So  far  as  we  know,  this 

flora  appears  to  have 

had  its  origin  in  eastern  or  northeastern  North  America,  in  the 

Patapsco  division  of  the  Potomac  series.  Although  the  great  ma- 
jority of  the  plants  found  in  associa- 
tion in  these  beds,  both  as  regards 
species  and  individuals,  still  belonged 
to  lower  Mesozoic  types,  such  as 
Ferns,  Cycads,  and  Conifers,  we  find 
ancient  if  not  really  ancestral  Angio- 
sperms. .  .  .  No  sooner  were  they 
(Angiosperms)  fairly  introduced  than 
they  multiplied  with  astonishing 
rapidity  and  in  the  .  .  .  Raritan 
they  had  become  dominant,  the 
Ferns  and  Cycads  having  mostly 
disappeared  and  the  Conifers  having 
taken  a  subordinate  position."  l  No 
present-day  species  existed,  but, 
among  the  more  modern  genera  were 
Oaks,  Elms,  Magnolias,  Maples, 
Figs,  Laurels,  Palms,  Grasses,  etc. 

1  F.  H.  Knowlton:  In  Outlines  of  Geologic  History,  by  Willis  and  Salisbury, 
pp.  205-206. 


Fig.  159 

A  Cretaceous  Brachiopod,  Tere- 
bratula  harlani.  Note  the 
curved  hinge  line.  (From 
Shimer's  "Introduction  to 
the  Study  of  Fossils,"  cour- 
tesy of  The  Macmillan  Com- 
pany.) 


258  HISTORICAL  GEOLOGY 

Later  Cretaceous  Angiosperms  were  remarkably  uniform  and 
widespread  over  the  earth. 

Protozoans.  —  The  Foraminifers  were  perhaps  more  prolific 
than  during  any  other  period.  Their  tiny  shells  practically  make 
up  the  great  chalk  beds,  especially  those  of  England,  France,  and 
the  Gulf  Coast  of  the  United  States. 

Porifers,  Coelenterates,  and  Echinoderms.  —  Among  these  the 
Sponges  were  common;  the  Corals  and  Crinoids  were  not  so  com- 
mon; while  the  Echinoids  were  abundant  and  diversified,  includ- 
ing both  the  regular  and  the  irregular  forms.  All  these  forms 
were  quite  modern  in  aspect. 

Molluscoids.  —  Since  these  organisms  had  previously  attained 
very  much  their  present-day  structures  and  subordinate  position 
among  the  invertebrates,  they  require  no  special  mention  here. 

Mollusks.  —  Pelecypods  continued  to  be  very  abundant,  with 
the  same  genera  of  the  Oyster  (Ostrea)  family  of  the  two  preceding 
periods  still  prominent.  In  addition  to  these  were  many  species 
of  the  characteristic  genera  Exogyra  and  Inoceramus  (see  Fig. 
160).  Many  of  the  other  genera,  often  of  modern  aspect,  were 
also  present. 

Gastropods  were  enriched  by  the  appearance  of  many  modern 
genera. 

Cephalopods.  The  Nautiloids  had  before  this  become  greatly 
reduced,  with  only  a  comparatively  few  coiled  forms  of  rather 
modern  aspect  left.  Ammonoids  continued  to  be  very  promi- 
nently represented  as  regards  both  numbers  of  species  and  indi- 
viduals, especially  by  the  Ammonites,  of  which  more  than  2000 
species  are  known  from  the  Mesozoic  alone.  Some  Cretaceous 
Ammonites  attained  a  diameter  of  several  feet.  During  the  Cre- 
taceous many  of  the  Ammonites  showed  a  remarkable  tendency 
to  assume  strange  forms  (Fig.  161).  Some  developed  uncoiled 
shells;  others  spiral  shapes;  while  still  others  were  curved  or 
actually  straight  (e.g.  Baculites).  Thus,  externally  at  least,  there 
was  a  reversion  to  the  early  Paleozoic  forms,  but  in  all  cases  they 
retained  their  complicated  suture  or  partition  structure.  "  These 
strange  forms  have  been  likened  by  Agassiz  to  death-contortions 
of  the  Ammonite  family;  and  such  they  really  seem  to  be.  .  .  . 
From  the  point  of  view  of  evolution,  it  is  natural  to  suppose  that 
under  the  gradually  changing  conditions  which  evidently  prevailed 
in  Cretaceous  times,  this  vigorous  Mesozoic  type  would  be  com- 


THE  CRETACEOUS  PERIOD 


259 


260 


HISTORICAL  GEOLOGY 


THE  CRETACEOUS  PERIOD  261 

pelled  to  assume  a  great  variety  of  forms,  in  the  vain  attempt  to 
adapt  itself  to  the  new  environment,  and  thus  to  escape  its  in- 
evitable destiny.  The  curve  of  its  rise,  culmination,  and  decline 
reached  its  highest  point  just  before  it  was  destroyed.  The  wave 
of  its  evolution  crested  and  broke  into  strange  forms  at  the  moment 
of  its  dissolution.'7 1  Very  few  if  any  Ammonites  crossed  the  line 
into  the  early  Cenozoic,  and  such  an  abrupt  termination  of  so 
abundant  and  diversified  a  group  of  animals  has  rarely  been  equaled 
in  the  history  of  the  animal  kingdom.  Belemnites  still  were  abun- 


Fig.  162 
A  Cretaceous  Teleost  Fish,  Osmeroides  Lewesiensis,  restored. 

dant  and  these,  too,  showed  a  remarkable  decline  by  the  close  of 
the  Cretaceous. 

Arthropods.  —  Broadly  considered,  the  Cretaceous  Arthropods 
were  much  like  those  of  the  Jurassic,  though  the  short-tailed 
Decapods  (Crabs)  increased  notably.  Most  of  the  Arthropods 
were  of  pretty  modern  aspect,  though  the  species  were  quite 
different  from  those  of  today. 

Fishes.  —  From  the  standpoint  of  evolution,  a  very  important 
change  took  place  among  the  Fishes.  Sharks  were  common,  having 
left  an  almost  incredible  number  of  fossil  teeth.  For  the  first  time 
the  Teleosts  (typical  bony  Fishes),  which  were  introduced  in  a 
small  and  primitive  way  in  the  Jurassic,  predominated  over  the 
Ganoids.  Many  Cretaceous  Teleosts  belonged  to  families  or  genera 
which  still  exist,  such  as  Salmon,  Herring,  Bass,  Cod,  etc.  Other 
types  were  more  characteristic  of  the  time. 

Amphibians.  —  These  were  of  quite  modern  appearance  and 
they  occupied  much  the  same  relatively  subordinate  position  that 
they  do  today. 

1  J.  Le  Conte:  Elements  of  Geology,  5th  ed.,  pp.  499-500. 


262 


HISTORICAL  GEOLOGY 


Reptiles.  —  Most  of  the  great  characteristic  groups  of  Jurassic 
Reptiles  continued  into  the  Cretaceous,  while  certain  new  forms, 
such  as  Mosasaurs,  Triceratops,  and  Snakes,  were  added.  Mesozoic 
Reptiles  are  discussed  at  the  end  of  this  chapter. 

Birds.  —  During  the  long  time  between  the  Jurassic,  when  the 
first  known  Birds  appeared,  and  the  Upper  Cretaceous,  important 
evolutionary  changes  took  place  in  this  class  of  animals,  though 
fossils  of  the  interval  are  almost,  if  not  wholly,  absent.  Creta- 
ceous Birds  were  distinctly  more  advanced  and  modern  in  appear- 
ance than  were  those  of  the 
Jurassic.  Thus  the  long,  verte- 
brated  tail  of  the  earlier  forms 
had  become  greatly  shortened, 
and  the  only  important  prim- 
itive characteristic  which  they 
retained  was  the  possession  of 
teeth.  Compared  with  modern 
Birds,  they  had  much  smaller 
brain  cavities. 

At  least  30  species  of  Cre- 
taceous Birds  are  known,  all 
of  these  belonging  to  two  great, 
though  very  different,  groups 
(orders)  e.g.  Ichthyornis  and 
Hesperornis.  All  appear  to 
have  been  aquatic  forms.  The 
Ichthyornis  types  were  power- 
ful fliers,  as  proved  by  the 
strongly  developed  keel  and 
wing  bones.  The  teeth  were 
set  in  distinct  sockets.  The 
structure  (biconcave)  of  their 

vertebrae  was  quite  distinctly  reptilian.    They  averaged  about  the 
size  of  a  pigeon  (see  Fig.  163). 

Hesperornis  comprised  forms  incapable  of  flight,  but  often  of 
great  size  —  five  to  six  feet  in  length.  In  marked  contrast  with  the 
Ichthyornis,  these  forms  had  powerfully  developed  legs  which 
served  as  swimming  paddles  in  these  almost  wholly  aquatic  forms. 
In  every  way  they  were  adapted  to  rapid  swimming.  Their  teeth 
were  set  in  grooves  instead  of  sockets. 


Fig.  163 

A  Cretaceous  toothed  Bird,  Ichthyornis 
victor.  Height,  about  9  inches.  (After 
Marsh.) 


THE  CRETACEOUS  PERIOD  263 

Mammals.  —  As  in  the  earlier  Mesozoic  periods,  the  Cretaceous 
Mammals  were  small,  primitive  forms  which  still  occupied  a  very 
subordinate  position  among  the  animals  of  the  time. 

MESOZOIC  REPTILES 

The  Mesozoic  era  has  been  appropriately  called  the  "Age  of 
Reptiles,"  since  those  animals  were  at  once  the  most  character- 
istic and  powerful  creatures  of  the  time.  So  far  as  known,  the  first 
true  Reptiles  appeared  in  the  Permian.  During  the  Mesozoic 
they  rose  to  great  prominence,  both  in  number  of  individuals  and 
diversity  and  size  of  forms;  reached  their  culmination  in  the 
midst  of  the  era;  and  declined  in  a  most  remarkable  manner  to- 
ward the  close  of  the  era.  During  the  Mesozoic  the  Reptiles 
ruled  all  fields  —  sea,  land,  and  air. 

"The  advance  from  the  Amphibian  to  the  Reptile  was  a  long 
forward  step  in  the  evolution  of  the  Vertebrates.  .  .  .  Yet  in 
advancing  from  the  Amphibian  to  the  Reptile  the  evolution  of  the 
Vertebrate  was  far  from  finished.  The  cold-blooded,  clumsy  and 
sluggish,  small-brained  and  unintelligent  Reptile  is  as  far  inferior 
to  the  higher  Mammals,  whose  day  was  still  to  come,  as  it  is  supe- 
rior to  the  Amphibian  and  the  Fish"  (W.  H.  Norton). 

The  Principal  Extinct  Mesozoic  Reptile  Groups 

The  following  grouping  of  the  more  characteristic,  extinct 
Mesozoic  Reptiles  is  not  meant  to  be  an  exact  scientific  classi- 

1.  Ichthyosaur  ("Fish-lizard"). 


1.  ENALIOSAURS  ("  Sea-lizards ")ee 
(Swimming  Reptiles). 


2.  DINOSAURS  ("Terrible-lizards") 
(Walking  Reptiles).       e.g. 


2.  Plesiosaur  ("Lizard-like"). 

3.  Mosasaur  ("Meuse  River  lizard") 

(Later  Mesozoic  only). 

1.  Sauropod  ("Lizard-footed") 

(Not  known  from  the  Triassic). 

2.  Stegosaur  ("Plated-lizard") 

(Not  known  from  the  Triassic). 

3.  Triceratops  ("  Three-horned  face")-** 

(Later  Mesozoic  only).       ' 

4.  Theropod  ("Beast-footed"). 

5.  Ornithopod  ("Bird-footed") 

(Not  known  from  the  Triassic). 


3.  PTEROSAURS  ("Winged-lizards")    ,  L  Pterodactyl  ("Winged-finger"). 

(Flying  Reptiles).          e.g.  j  2    Ramphorhyncus  ("Beaked-snout"). 


264 


HISTORICAL  GEOLOGY 


Fig.  164 

A  group  of  Ichthyosaurs,  Ichthyosaurus  quadricissus,  of  the  Enaliosaur  division 
of  Mesozoic  Reptiles.  Maximum  length  25  to  30  feet.  Restoration  by 
C.  R.  Knight,  under  the  direction  of  H.  F.  Osborn.  (By  permission  of  the 
American  Museum  of  Natural  History.) 


THE  CRETACEOUS  PERIOD  265 

fication,  but  rather  it  is  a  simple  arrangement  for  convenience  of 
elementary  discussion.  Unless  otherwise  stated  the  types  men- 
tioned ranged  through  the  whole  Mesozoic. 

Enaliosaurs.  —  There  are  many  known  types  of  these  swim- 
ming Reptiles,  but  only  a  few  of  the  most  typical  and  characteristic 
forms  are  chosen  for  description. 

The  Ichthyosaurs  were  Fish-like  forms  which  ranged  in  length 
up  to  25  or  30  feet.  They  had  stout  body,  very  short  neck,  and 
very  large  head  (see  Fig.  164).  The  head,  sometimes  4  or  5  feet 
long,  had  an  elongate  snout  in  which  as  many  as  200  large  sharp 
teeth  were  set  in  grooves  (not  in  sockets) .  Enormous  eyes,  some- 
times over  a  foot  in  diameter,  were  protected  by  bony  plates.  A 
powerful  tail  with 
two  lobes  set  ver- 
tically  had  the 
vertebral  column 
extending  through 
the  lower  lobe. 
The  four  limbs 
were  perfectly  con-  Fig  165 

verted  into  swim-  A  well.preserved  ichthyosaur  found  in  Germany, 
mmg  paddles,  thus  (After  Fraas.) 

strongly  suggesting 

that  these,  as  well  as  other  Enaliosaurs,  represent  former  land 
Reptiles  which  adapted  themselves  to  a  water  environment  much 
like  certain  Mammals  of  today,  such  as  Whales  and  Dolphins. 
Fishes  and  Cephalopods  were  largely  their  prey,  as  proved  by  the 
fossil  contents  of  their  stomachs,  no  less  than  200  Belemnite 
remains  having  been  found  in  one  specimen  alone.  Many  remark- 
ably preserved  specimens  of  Ichthyosaurs  have  been  discovered 
(Fig.  165),  some  with  even  the  embryos  plainly  visible  within  the 
bodies.  Ichthyosaurs  ranged  through  the  whole  Mesozoic. 

Plesiosaurs  were  less  powerful  forms  than  Ichthyosaurs, 
though  they  were  usually  longer,  some  having  attained  a  maximum 
length  of  40  to  50  feet  (Fig.  166).  A  stout  body,  long  slender 
neck,  small  head,  short  tail,  and  four  powerful  paddles  were  char- 
acteristic features.  Sharp  teeth  were  set  in  sockets  (not  grooves) 
in  the  jaws.  With  their  slender,  serpent-like  necks,  often  10  to 
20  feet  long,  "the  Plesiosaurs  could  lie  motionless  far  below  the 
surface,  occasionally  raising  their  heads  above  the  water  to  breathe, 


266  HISTORICAL  GEOLOGY 

or  darting  them  to  the  bottom  after  their  prey,  which  consisted 
chiefly  of  Fish"  (W.  B.  Scott).  Plesiosaurs  ranged  through  the 
whole  Mesozoic. 

Mosasaurs  were  literal  "  sea-serpents "  or  carnivorous  marine 
Reptiles  which  often  reached  a  length  of  from  40  to  75  feet  (Fig. 
167).  Though  now  wholly  extinct,  they  were  closely  related  to 
Snakes  and  Lizards  in  structure.  The  four  limbs  were  converted 


Fig.  166 

A  restored  Plesiosaur,  Plesiosaurus  dolichodeirus,  of  the  Enaliosaur 
division  of  Mesozoic  Reptiles.  Maximum  length  40  to  50  feet. 
(From  Le  Conte's  "  Geology,"  courtesy  of  D.  Appleton  and  Com- 
pany.) 

into  short,  stout,  swimming  paddles,  and  their  jaws  were  set  with 
sharp  teeth.  The  relatively  smaller  head,  long,  slender  body,  and 
different  tail  structure  distinguish  the  Mosasaurs  from  the  Ichthyo- 
saurs,  as  a  comparison  of  the  accompanying  pictures  will  show. 
Mosasaurs  existed  during  the  latter  portion  only  of  the  Mesozoic. 

Dinosaurs.  —  These  Mesozoic  Reptiles  comprised  a  great 
variety  of  forms  both  as  regards  shape  and  size.  Only  five  of  the 
more  common  and  characteristic  types  have  been  selected  for 
description. 

The  Sauropods  were  the  largest  of  all  Mesozoic  Reptiles,  and 
in  fact  they  included  the  largest  animals  which  ever  trod  the  earth. 
Well-preserved  specimens  are  known  whose  lengths  are  from  75  to 
90  feet,  and  recently  one  has  been  discovered  in  Utah  which  it  is 


THE  CRETACEOUS  PERIOD 


267 


thought  will,  when  mounted,  show  a  length  of  over  100  feet.  It 
has  been  estimated  that  one  of  these  large  brutes  must  have 
weighed  about  40  tons.  Note  the  extremely  long  neck  and  tail, 
very  small  head,  and  strong  bones  of  the  four  great  legs.  Thigh 
bones  7  feet  long  are  known.  They  were  five-toed  and  plantigrade, 
and  doubtless  walked  with  body  well  above  ground  (Fig.  168). 


Fig.  167 

A  Mosasaur,  Tylosaurus  dyspelor,  of  the  Enaliosaur  division  of  Mesozoic 
Reptiles.  Maximum  length  about  75  feet.  Restoration  by  C.  R.  Knight 
under  the  direction  of  H.  F.  Osborn.  (Courtesy  of  the  American  Museum 
of  Natural  History,  from  Scott's  "Geology,"  by  permission  of  The 
Macmillan  Company.) 

All  were  plant-eaters  and  provided  with  grinding  teeth.    Sauropods 
ranged  through  all  the  Mesozoic  except  the  Triassic. 

The  Stegosaurs  are  so  named  because  of  the  double  row  of  great 
bony  plates  on  the  back  of  eaclj  of  these  most  remarkable  brutes 
(Fig.  169)  which  attained  a  maximum  length  of  30  to  40  feet.  The 
long,  powerful  tail  had  several  pairs  of  long  spines  toward  the  end 
instead  of  plates.  As  compared  with  the  Sauropods  the  neck  was 
short.  They  were  quadrupedal,  four-toed  in  front,  and  three-toed 


268 


HISTORICAL  GEOLOGY 


in  the  rear.  All  were  plant-eaters.  The  brains  of  all  Dinosaurs 
were  almost  incredibly  small,  even  as  compared  with  modern 
Reptiles,  and  "this  was  especially  true  of  Stegosaurs.  To  make  up 
for  this  deficiency  they  had  an  enormous  enlargement  of  the 
spinal  cord  in  the  sacral  region  (i.e.  over  the  hind  legs).  This 
sacral  brain  —  if  we  may  so  call  it  —  was  ten  to  twenty  times 


Fig.  168 

The  hugeji  of  all  known  Dinosaurs,  a  Sauropod,  Diplodocus.  A  mounted 
skeleton  in  the  Carnegie  Museum  of  Pittsburg  measures  87  feet  long. 
Restored  by  C.  R.  Knight  under  the  direction  of  H.  F.  Osborn.  (Courtesy 
of  the  American  Museum  of  Natural  History.) 

bigger  than  the  cranial  brain.  It  was  necessary  in  order  to  work 
the  powerful  hind-legs  and  tail"  (J.  LeConte).  Stegosaurs  existed 
through  all  of  the  Mesozoic  except  the  Triassic. 

Triceratops  was  another  strange-looking  creature,  so  named 
because  of  its  three  horns  —  two  of  great  size  just  back  of  the  eyes 
and  a  smaller  one  on  the  nose  (see  Fig.  170).  The  enormous 
flattened  skull  had  a  sharp  beak  in  front.  The  skull  extended 
backward  into  an  immense  hood  or  cape-like  structure.  According 
to  Marsh  they  (Triceratops)  had  the  largest  heads  and  smallest 
brains  of  the  Reptiles,  and  hence  they  must  have  been  exceedingly 
stupid.  Skulls  6  or  8  feet  long  have  been  found.  The  four  legs 


THE  CRETACEOUS  PERIOD 


269 


Fig.  169 

A  Stegosaur,  an  armored  Dinosaur.  Maximum  length  30  to  40  feet.  Re- 
stored by  C.  R.  Knight.  (By  permission  of  F.  A.  Lucas  and  Doubleday, 
Page  and  Company,  and  courtesy  of  Henry  Holt  and  Company.) 

and  the  tail  were  massive  and  powerful.     This  creature  attained  a 
length  of  fully  25  feet,  and  it  had  a  bulk  about  twice  that  of  an 


Fig.  170 

A  Triceratops,  Triceratops  prorsus,  of  the  Dinosaur  division  of 
Mesozoic  Reptiles.  Maximum  length  25  feet.  (Skeleton  re- 
stored by  Marsh.) 


270 


HISTORICAL  GEOLOGY 


Elephant.  It  was  a  plant-eater  and  probably  not  as  ferocious  a' 
it  looked.  Good  specimens  have  been  found  in  the  western  in- 
terior of  the  United  States.  Tricerat ops, existed  only  during  the 
Cretaceous  period. 

Theropods  were  carnivorous  Dinosaurs,  as  proved   by  their 
numerous  sharp  teeth  set  in  comparatively  large  beads  (see  Fig. 


Fig.  171 

Theropods,  Allosaurus  agilis,  of  the  Dinosaur  division  of  Mesozoic  Reptiles. 
Restored  by  C.  R.  Knight,  under  the  direction  of  H.  F.  Osborn.  (Cour- 
tesy of  the  American  Museum  of  Natural  History.) 

171).  They  were  bipedal,  that  is  they  walked  on  two  legs,  the 
front  limbs  having  been  very  small  and  used  only  for  grasping. 
The  toes  were  armed  with  sharp  claws.  The  bipedal  habit  Com- 
bined with  the  long,  ponderous  tail  gave  them  a  sort  of  Kangaroo 
aspect.  The  limb  bones  were  hollow,  thus  suggesting  a  bird-like 
structure.  In  fact  before  if  was  known  that  the  numerous  tracks 
in  the  Newark  sandstone  of  the  Connecticut  Valley  were  made  by 
creatures  of  tbis  sort,  they  were  called  " Bird-tracks."  Theropods 
reached  a  length  of  fully  15  feet,  and  though  much  smaller  than 
many  other  Dinosaurs,  they  were  probably  the  most  ferocious  of 
all  and  more  than  likely  preyed  upon  even  the  much  larger  plant- 


THE  CRETACEOUS  PERIOD  271 

Caters.     The  Theropods  lived  through  the  whole  Mesozoic,  and 
they  have  been  found  in  many  parts  of  the  world. 

Ornithopods  were  in  general  appearance  much  like  the  Thero- 
pods, but  they  were  certainly  plant-eaters,  as  shown  by  the  tooth 
structure  (see  Fig.  173).  They  were  bipedal,  the  hind  limbs 
having  only  three  functional  toes,  giving  a  sort  of  bird-like  track. 
The  largest  of  these  creatures  measured  30  feet  in  length,  and  when 
walking  they  must  have  stood  15  or  20  feet  high.  Ornithopods 
ranged  through  all  the  Mesozoic  except  the  Triassic. 


Fig.  172 

A  small  two-legged  Dinosaur,  Podokesaurus  holyokensis 
(Talbot),  from  the  Triassic  of  Massachusetts.  Length, 
less  than  4  feet.  Restored  by  Lull.  (From  a  photo- 
graph by  Mrs.  E.  H.  Terry  of  the  model  at  Mount 
Holyoke  College.) 

Pterosaurs.  —  These  were  literal  "flying-dragons"  in  Meso- 
zoic time.  They  varied  greatly  in  size  from  about  that  of  a 
sparrow  to  others  with  a  spread  of  wing  of  25  feet,  which  is  about 
twice  that  of  any  modern  Bird.  Not  only  did  they  include  the 
largest  creatures  which  ever  flew  but,  on  account  of  their  hollow 
bones,  their  skeletons  were  wonderfully  light.  One  finger  of  each 
front  limb  was  enormously  lengthened  to  support  the  flying 
membrane,  as  shown  in  Fig.  174.  The  other  fingers  were  armed 
with  sharp  claws.  In  general  we  may  recognize  two  groups. 
One  group  was  typified  by  the  Pterodactyl,  which  had  a  short, 
stout  body,  short  tail,  and  moderately  long  neck.  The  earlier 
Mesozoic  forms  were  supplied  with  sharp  teeth,  while  the  Creta- 
ceous forms  were  mostly  toothless.  The  other  group,  typified  by  the 
Rhamphorhyncus  (Fig.  174),  had  long  tail,  and  in  one  species  at  least 


272 


HISTORICAL  GEOLOGY 


the  end  of  the  tail  was  expanded  into  a  sort  of  rudder.    Many 
wonderfully  preserved  specimens  of  Pterosaurs  have  been  found, 


Fig.  173 

An  Ornithopod,  Claosaurus  annectens,  of  the  Dinosaur 
division  of  Mesozoic  Reptiles.  Length  over  20  feet. 
(Skeleton  restored  by  March.) 

some  with  even  the  wing  membranes  preserved.    Pterosaurs  ranged 
from  the  late  Triassic  to  the  close  of  the  Mesozoic. 


Fig.  174 

A  Rhamphorhynchus  of  the  Pterosaur  division  of  Mesozoic  Reptiles. 
Spread  of  wing  about  2  feet.     (Restored  by  Marsh.) 


THE  CRETACEOUS  PERIOD  273 

• 

The  Principal  Surviving  Mesozoic  Reptile  Groups 

Though  overwhelmed  by  the  Reptiles  above  described  and  of 
less  peculiar  interest  because  they  represent  groups  still  living, 
certain  other  Mesozoic  Reptiles  deserve  brief  mention. 

Turtles  date  back  at  least  to  the  middle  Triassic,  and  even 
those  very  early  forms  clearly  showed  the  familiar  structure  which 
easily  separates  them  from  other  Reptiles. 

Lizards  are  known  even  from  the  Triassic,  and,  though  they 
ranged  through  the  Mesozoic,  they  were  always  small  and  com- 
paratively rare. 

Crocodiles  made  their  first  appearance  in  the  Jurassic,  and  some 
were  marine  forms.  In  appearance  they  resembled  the  modern 
Gavial  of  India,  particularly  as  regards  the  long,  slender  snout. 
Crocodiles  were  numerous  from  the  Jurassic  to  the  end  of  the 
Mesozoic. 

Snakes  are  not  known  to  have  appeared  till  late  in  theXJre- 
taceous,  and  those  early  forms  were  small  and  comparatively  rare. 


CHAPTER  XVII 
SUMMARY    OF    MESOZOIC    HISTORY 

ALTHOUGH  the  Mesozoic  was  quite  certainly  shorter  than  the 
Paleozoic,  it  must,  nevertheless,  have  had  a  duration  of  at  least 
some  millions  of  years.  As  the  name  indicates,  the  Mesozoic  was 
the  era  of  transition  between  the  Paleozoic  and  the  Cenozoic. 
Eastern  North  America  had  been  to  a  large  degree  completed  at 
the  time  of  the  Appalachian  Revolution,  except  for  the  addition  of 
the  Atlantic  and  Gulf  Coastal  Plain  belts.  In  western  North 
America,  however,  profound  physical  geography  changes  took 
place,  bringing  that  part  of  the  continent  almost  to  its  present 
condition,  as  regards  relations  of  land  and  sea,  only  near  the  close 
of  the  Mesozoic.  The  life  of  the  Mesozoic,  too,  was  distinctly 
intermediate  in  character,  those  of  the  great  groups  of  character- 
istic Paleozoic  organisms  which  did  continue  into  the  Mesozoic 
having  become  extinct  during  the  era,  while  many  more  modern 
groups  showed  great  development  during  the  era.  Certain  other 
important  groups  of  organisms  like  the  Cycads,  Ammonites,  and 
Reptiles,  were  eminently  characteristic  of  the  Mesozoic  and  reached 
their  culmination  during  the  era. 

MESOZOIC  ROCKS 

The  late  Triassic  stratified  rocks  of  the  Atlantic  Coast  are 
sandstones,  conglomerates,  and  shales,  mostly  of  continental  origin, 
though  in  part  at  least  probably  of  estuarine  origin.  Rocks  of  the 
Triassic  in  the  western  interior  are  chiefly  the  Red  Beds  (shales, 
sandstones,  and  limestones),  with  more  or  less  salt  and  gypsum,  of 
terrestrial  or  lacustrine  origin.  On  the  Pacific  Coast  the  strata  are 
of  true  marine  origin  and  they  consist  of  all  sorts  of  typical  sedi- 
ments. 

Jurassic  strata  are  wholly  confined  to  the  western  interior  and 
Pacific  borders,  where  they  are  all  typical  marine  sediments,  except 
the  earlier  Jurassic  beds  of  the  western  interior,  which  are  of  con- 
tinental origin  and  probably  also  include  some  Red  Beds. 

274 


SUMMARY  OF  MESOZOIC  HISTORY  275 

Lower  Cretaceous  strata  occur  on  the  Atlantic  and  eastern 
Gulf  coasts,  where  they  consist  almost  entirely  of  unconsolidated 
sands  and  clays  of  continental  origin.  The  Lower  Cretaceous 
strata  in  the  Texan  region  are  made  up  chiefly  of  more  or  less 
consolidated  sands,  sandstones,  and  chalky  limestones  of  marine 
origin,  with  continental  deposits  at  the  base.  In  the  western 
interior  regions  of  both  the  United  States  and  Canada,  the  strata 
rather  doubtfully  of  this  age  are  probably  of  continental  origin. 
On  the  Pacific  Coast  there  are  great  thicknesses  of  marine  Lower 
Cretaceous  strata  of  rather  restricted  occurrence. 

Upper  Cretaceous  deposits  of  the  Atlantic  and  eastern  Gulf 
regions  are  mostly  sands,  clays,  marls,  and  greensands,  with  some 
chalky  limestones  toward  the  south.  These  are  very  largely  of 
marine  origin.  In  Texas  and  the  western  interior  the  Upper  Cre- 
taceous beds  are  there  mostly  marine  sandstones,  shales,  and  chalky 
limestones,  though  some  continental  deposits  (including  coal) 
also  occur,  especially  in  the  latest  Cretaceous.  On  the  Pacific 
Coast  typical  marine  beds  occur. 

Some  igneous  rocks  of  Triassic  age  occur  on  the  Atlantic  Coast, 
while  great  quantities  of  Cretaceous  igneous  rocks  occur  in  the 
Pacific  northwest. 

In  general  the  thickness  of  the  Mesozoic  group  of  rocks  is  not 
nearly  as  great  as  that  of  the  Paleozoic,  but  more  locally  remarkable 
thicknesses  of  strata  are  represented  in  even  single  systems,  as  in 
the  case  of  the  Triassic  beds  of  the  Atlantic  border  (10,000  to 
15,000  feet  thick),  or  the  Lower  Cretaceous  beds  of  the  Pacific 
border  (fully  26,000  feet  thick). 

PHYSICAL  HISTORY 

Relations  of  Land  and  Sea.  —  Throughout  the  era,  except 
during  the  Cretaceous,  North  America  was  mostly  dry  land,  thus 
being  in  marked  contrast  with  the  Paleozoic  condition  of  the  con- 
tinent. The  eastern  half  or  two-thirds  of  the  continent,  except 
the  Atlantic  and  Gulf  borders,  was  continually  dry  land,  while  the 
western  side  of  the  continent  was  subject  to  varying  marine, 
estuarine,  and  lacustrine  conditions.  The  reader  should  review 
the  paleogeographic  maps. 

At  the  opening  of  the  Mesozoic  era,  or  Triassic  period,  eastern 
North  America  was  all  dry  land;  continental  (partly  lacustrine) 


276  HISTORICAL  GEOLOGY 

deposits  were  forming  in  the  western  interior  of  the  United  States; 
and  the  Pacific  border  was  mostly  occupied  by  marine  waters. 
Later  in  the  Triassic  the  same  conditions  prevailed  in  the  west, 
but  long,  narrow  troughs  were  formed  along  the  Atlantic  side  in 
which  were  accumulated  the  thick  continental  and  estuarine 
(Newark)  deposits.  Map  figure  123  shows  the  condition  of  the 
continent  at  that  time.  At  the  close  of  the  Triassic,  or  beginning 
of  the  Jurassic,  there  was  enough  crustal  movement  to  convert  the 
basins  (Newark)  of  deposition  in  the  east  into  dry  land,  while  in  the 
west  the  conditions  appear  to  have  continued  as  during  the  period. 

During  the  earlier  Jurassic  the  conditions  just  described  in  the 
west  still  prevailed,  but  in  the  later  Jurassic  a  transgression  of  the 
sea  took  place  from  British  Columbia  southward  over  the  Rocky 
Mountain  region  as  far  as  northern  Arizona  (see  map  Fig.  133). 
During  the  whole  Jurassic  eastern  North  America  was  land  under- 
going erosion  toward  the  peneplain  condition. 

During  the  Lower  Cretaceous  there  was  enough  subsidence  of 
the  Atlantic  and  eastern  Gulf  borders  to  produce  flood-plains, 
lakes,  and  marshes  in  which  were  deposited  the  Potomac  series  of 
sands,  gravels,  clays,  etc.  About  the  same  time  the  continental 
(Trinity)  deposits,  followed  by  the  marine  Fredericksburg  and 
Washita  beds,  were  accumulating  over  the  western  Gulf  (Texan) 
regions  and  southern  western  interior  regions,  and  continental 
deposits  were  forming  over  the  northern  western  interior  region 
just  west  of  the  site  of  the  Rockies.  During  the  Lower  Creta- 
ceous on  the  Pacific  border  there  were  accumulated  very  thick 
marine  deposits  just  west  of  the  newly  formed  Sierras,  especially  in 
the  Great  Valley  of  California.  Marine  deposition  also  took  place 
along  some  of  the  coast  north  of  California. 

The  Lower  Cretaceous  closed,  or  the  Upper  Cretaceous  opened, 
with  the  eastern  part  of  the  continent  all  undergoing  erosion;  a 
continuance  of  marine  waters  over  the  western  Gulf  (Texan)  and 
southern  western  interior  regions;  and  some  deformation  (folding 
and  faulting)  of  the  strata  in  parts  of  the  Coast  Range  district. 

At  the  opening  of  the  Upper  Cretaceous  the  condition  of  the 
continent  was  essentially  that  just  described  for  the  close  of  the 
Lower  Cretaceous.  Early  in  the  Upper  Cretaceous,  marine  waters 
spread  over  practically  all  of  the  Atlantic  and  eastern  Gulf  Coastal 
Plain  areas.  At  the  same  time  "Appalachia,"  which  had  been  so 
long  persistent,  became  submerged,  not  again  to  reappear.  The 


SUMMARY  OF  MESOZOIC  HISTORY  277 

Texan  and  western  interior  areas  were  marked  by  the  deposition 
of  the  largely  continental  (Dakota)  sandstone  early  in  the  period. 
At  the  same  time  the  western  edge  of  the  continent  was  submerged 
under  the  sea. 

In  later  Upper  Cretaceous  time,  the  Atlantic  Coast  and  eastern 
Gulf  districts  continued  much  as  in  the  earlier  Upper  Cretaceous. 
The  western  Gulf  and  western  interior  districts,  however,  were 
marked  by  a  vast  transgression  of  the  sea  from  the  Gulf  to  the 
Arctic,  while  the  Pacific  border  continued  as  earlier  in  the  Upper 
Cretaceous.  Map  Fig.  151  shows  the  condition  of  the  continent  in 
this  later  Cretaceous  time. 

Mountain  Making.  —  The  Jurassic  period  was  closed  in  the 
west  by  the  " Sierra  Nevada  Revolution,"  when  strata  of  great 
thickness  were  folded  into  mountains  along  the  present  site  of  the 
Sierras  and  probably  also  the  Cascades.  There  was  also  some 
deformation  in  the  region  of  the  Coast  Ranges. 

The  Mesozoic  era  was  closed  by  one  of  the  most  profound 
physical  disturbances  in  the  post-Algonkian  history  of  North 
America,  if  not  in  the  world,  —  the  "Rocky  Mountain  Revolu- 
tion," —  when  strata  were  more  or  less  deformed  by  folding  and 
faulting  throughout  much  of  the  Rocky  Mountain  system.  At 
the  same  time  the  whole  eastern  side  of  the  United  States,  includ- 
ing the  Appalachians,  which  had  been  worn  down  to  a  peneplain, 
was  distinctly  upraised  without  renewed  folding  of  the  rocks. 

Vulcanism.  —  While  the  later  Triassic  (Newark)  sandstones 
were  forming  on  the  Atlantic  Coast,  there  were  considerable  in- 
trusions and  extrusions  of  igneous  rocks,  now  represented  by  such 
masses  as  the  Palisades  of  the  Hudson  and  the  Holyoke  Range  of 
Massachusetts. 

Accompanying  the  Rocky  Mountain  Revolution  there  were 
tremendous  outpourings  of  lava  in  the  northwestern  portion  of 
the  United  States. 

CLIMATE 

The  character  and  distribution  of  organic  remains,  both  plant 
and  animal,  pretty  clearly  prove  the  climate  of  the  Mesozoic  to 
have  been  mild  to  possibly  even  warm  temperate,  with  an  appre- 
ciable distinction  of  climatic  zones,  though  not  at  all  comparable 
to  those  of  the  present.  Warm  temperate  plants  of  the  Cretaceous 
are  found  even  within  the  Arctic  circle. 


278  HISTORICAL  GEOLOGY 

TABULAR  SUMMARY  OF  MESOZOIC  LIFE 


Plants 

Protozoans 

Porifers  and 
Ccelenterates 

Echinoderms 

Cryptogams  and 

Crinoids:    Greatly    *- 

Gymnosperms: 

reduced. 

CRETACEOUS 

Much  like  earlier 
Mesozoic. 
Angiosperms  :  Mono- 
cotyledons and   Di- 
cotyledons attain 

Foraminifers 
and  Radiolari- 
ans:  Profuse. 

Sponges  and  Corals: 
Abundant  and 
much  like  those  of 
the  Jurassic. 

Asterozoans:    Pres- 
ent. 

Echinoids:    Both 

supremacy  among 

regular  and  irregu- 

plants. 

lar  forms  common. 

Crinoids:    Very  pro- 

Cryptogams:    Much 
like  Triassic. 
Gymnosperms:      Cy- 

Foraminifers 
and 

Sponges:  Very 
abundant. 

fuse    and    notably 
large. 
Asterozoans:      Pres- 

JURASSIC 

cads  culminate; 
Conifers  more  mod- 
ern in  aspect. 
Angiosperms: 
Monocotyledons? 

Radiolarians  : 
Very  abundant 
and  highly  di- 
versified. 

Corals:   Abundant 
and   all   are   Hexa- 
coralla    of    modern 
appearance. 

ent  and  of  modern 
appearance. 
Echinoids:    Abun- 
dant, with  first  ir- 
regular, more  mod- 

ern forms. 

Thallophytes. 

TRIASSIC 

Bryophytes. 
Pteridophytes:      Ly- 
copods    almost    ex- 
tinct;   Ferns  and 
Equiseta?    common. 
Gymnosperms:    Cor- 
daites    become    ex- 
tinct;   Cycads    and 

Foraminifers 
and 
Radiolarians: 
Present. 

Sponges:  Present. 
Corals:    Very  abun- 
dant, especially  the 
more  modern  Hexa- 
coralla  ;      ancient 
Tetracoralla    be- 
come extinct. 

Crinoids:  Common. 
Asterozoans: 
Present. 
Echinoids:  Common 
and  all  are  regular 
forms  of  ancient  as- 
pect. 

Conifers  prominent. 

In  early  Mesozoic  time  arid  climate  conditions  must  have  pre- 
vailed over  the  western  interior  of  the  United  States,  as  shown  by 
the  Red  Beds  with  some  salt  and  gypsum. 

There  is  no  good  evidence  of  glaciation  in  the  Mesozoic. 

ORGANIC  HISTORY 

"The  life  of  the  Mesozoic  constitutes  a  very  distinctly  marked 
assemblage  of  types,  differing  both  from  their  predecessors  of  the 
Paleozoic  and  their  successors  of  the  Cenozoic.  In  the  course  of 
the  era  the  plants  and  marine  invertebrates  remain  throughout  the 
era  very  different  from  later  ones.  Even  in  the  Vertebrates,  how- 
ever, the  beginning  of  the  newer  order  of  things  may  be  traced."  L 
1  W.  B.  Scott:  Introduction  to  Geology,  2nd  ed.,  p.  655. 


SUMMARY  OF  MESOZOIC  HISTORY  279 

TABULAR  SUMMARY  OF   MESOZOIC   LIFE  — Continued 


Molluscoids 

Mollusks 

Arthropods 

Vertebrates 

Bryozoans: 
Present. 

Brachiopods:   Only 
a  few  genera  and 
species  remain, 
and  these   are   of 
pretty  modern  as- 
pect.                    ^ 

Pelecypods    and    Gastro- 
pods: Abundant  and  sim- 
ilar to  Jurassic,  but  more 
modern. 
Cephalopods:     Still    very 
abundant  and  much  like 
those  of  the  Jurassic  with 
uncoiled  to  even  straight 
Ammonoids    (e.g.  Bacu- 
lites)  common.     Ammo- 
x-noids  become  nearly  ex- 
tinct.    Dibranchs    com- 
mon. 

Eucrustaceans:  Much 
like  Jurassic,  but 
Brachyurans  (Crabs) 
greatly  increased.  _ 

[nsects:     Much     like 
Jurassic     but     even 
more  modern  types 
appear. 

Fishes:   Selachians   abun- 
dant;    Dipnoans     rare;      / 
Ganoids  common;   Tele- 
osts  predominate. 
Amphibians:     Very    sub-  — 
ordinate. 
Reptiles:    Abundant   and  f 
much  like  Jurassic;  first  ; 
Snakes. 
Birds:  Much  increased. 
Mammals:  Simple,  rare.    - 

Bryozoans: 
Present. 

Brachiopods:     Still 
more     diminished 
and  not  many  spe- 
cies. 

Pelecypods:      Similar    to 
Triassic,  but  increased. 
Gastropods:  Ditto. 
Cephalopods:    Nautiloids 
of  coiled  forms  only  and 
common;  Ammonoids 
(e.g.  Ammonites)  culmi- 
nate, with  development 
of  some  uncoiled  to  even 
straight    forms;    Di- 
branchs become  profuse 
(e.g.  Belemnites). 

Eucrustaceans:     Ma- 
crurans     (e.g.     Lob- 
sters)  common,  and 
Brachyurans   (e.g. 
Crabs)   first  appear, 
though  rare. 
Insects:    Abundant 
and  diversified;   first 
appearance  of  high- 
est forms,  e.g.  Flies, 
Ants  and  Bees. 

Fishes:     Selachians  com- 
mon;     Dipnoans     rare; 
Ganoida  common;   Tele- 
osts    first    appear,    but 
rare. 
Amphibians:   Fossils? 
Reptiles:   Much  like  Tri- 
assic, but  more  common 
and  varied. 
Birds:    First  appear  (e.g.     »/ 
Archeopteryx)  .        Mam-      jf 
mals:  Simple,  rare. 

Bryozoans: 
Present. 

Brachiopods: 
Greatly  dimin- 
ished   and    those 
with  curved-hinge 
lines    prevail    for 
the  first  time. 

Pelecypods    and    Gastro- 
pods: Prominent  and  as- 
sume    more      distinctly 
modern  aspect. 
Cephalopods:  .  Nautiloids 
common,    with    straight 
forms    (Orthoceras)    be- 
coming extinct;   Ammo- 
noids common,  with  com- 
plex sutures  (e.g.   Cera- 
tites    and    Ammonites)  ; 
Dibranchs  first  appear. 

Eucrustaceans  :     Ma- 
crurans     (e.g.     Lob- 
sters) first  appear. 

Insects:    Common 
and   mostly   simpler 
forms  but  first  Bee- 
tles appear. 

Fishes:    Selachians,   Dip- 
noans and  Ganoids  much 
as  in  late  Paleozoic  time. 
Amphibians:       Declining 
but  large. 
Reptiles:    Abundant   and 
varied,  e.g.  Enaliosaurs, 
Dinosaurs,     and     Ptero- 
saurs; first  Turtles  and 
Lizards. 
Mammals  :  First  and  rare.    /\ 

Among  plants  the  Ferns,  Cycads,  and  Conifers  predominated 
during  the  earlier  Mesozoic,  but  later  in  the  era  the  Angiosperms, 
including  both  Monocotyledons  and  Dicotyledons,  first  appeared 
and  very  soon  predominated. 

Among  animals  the  absence  of  certain  characteristic  Paleozoic 
groups  should  be  noted,  such  as  Cystoids,  Blastoids,  Trilobites, 
and  Eurypterids.  Other  Paleozoic  groups  continued  into  the  early 
Mesozoic  and  then  either  became  extinct  or  very  greatly  diminished 
such  as  the  ancient  Corals  (Tetracoralla),  Brachiopods,  Orthoceras, 
and  Amphibians.  Some  of  the  more  important  groups  which  made 
their  first  appearance  in  the  Mesozoic  were  modern  Corals  (Hexa- 
coralla),  modern  Echinoids  (e.g.  Sea-urchins),  modern  Eucrusta- 
ceans (e.g.  Lobsters  and  Crabs),  highest  Insects,  Teleost  Fishes, 


280  HISTORICAL  GEOLOGY 

primitive  Birds,  and  small,  primitive  Mammals.  Reptiles,  which 
began  in  the  very  late  Paleozoic,  developed  marvellously  during 
the  era,  thus  justifying  the  application  of  the  term  "Age  of 
Reptiles"  to  the  Mesozoic. 

On  the  accompanying  chart  the  author  has  brought  together 
in  concise  form  the  salient  facts  regarding  the  life  of  the  Mesozoic. 
In  regular  order,  the  principal  successive  changes  in  the  sub- 
kingdoms  and  classes  of  plants  and  animals  are  graphically  repre- 
sented. 


CENOZOIC  ERA 


CHAPTER  XVIII 

THE  TERTIARY  PERIOD 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

THE  Cenozoic  era  is  often  called  the  "Age  of  Mammals"  be- 
cause, for  the  first  time,  these  most  highly  organized  of  all  animals 
became  abundant  and  diversified  and  were  masters  of  the  land. 
Plants  and  animals  both  took  on  a  decidedly  modern  aspect,  with 
species  of  living  organisms  represented  for  the  first  time,  some  even 
in  the  early  Cenozoic  and  many  during  the  later  portion  of  the  era. 

The  name  "Tertiary"  has  entirely  lost  its  original  significance, 
but  has,  nevertheless,  become  thoroughly  fixed  in  the  literature  of 
geology.  In  the  early  days  of  the  science,  the  whole  known 
geological  column  was  divided  into  three  groups  of  rocks,  and  later 
into  four  groups,  namely:  Primary,  Secondary,  Tertiary,  and 
Quaternary.  After  the  discovery  of  rocks  still  older  than  these,  the 
term  Primary  was  replaced  by  Paleozoic ;  Secondary  by  Mesozoic ; 
while  Tertiary  and  Quaternary  have  been  retained  as  subdivisions 
of  the  Cenozoic. 

Following  are  the  subdivisions  of  the  Tertiary  system  now 
recognized  as  world-wide  in  application: 


TERTIARY 

SYSTEM 


Pliocene  series 
("More  recent"). 

Miocene  series 
("Less  recent"). 

Oligocene  series 
("Little  recent"). 

Eocene  series 

"Dawn  of  recent"). 


Upper  Tertiary. 


Lower  Tertiary. 


Sir  Charles  Lyell  first  divided  the  Tertiary  into  Eocene,  Miocene, 
and  Pliocene  on  the  basis  of  percentage  of  living  species  repre- 
sented in  each  series,  there  being  very  few  in  the  earliest  and  a 

281 


282 


HISTORICAL  GEOLOGY 


very  large  percentage  in  the  latest  series.  Later  the  Oligocene  was 
added  by  combining  some  of  the  uppermost  Eocene  with  some  of 
the  lowermost  Miocene,  though  in  North  America  the  term  Oligo- 
cene has  been  but  little  used  till  very  recently,  and  even  now  such 
strata  are  not  always  separately  differentiated. 

Following  are  the  principal  subdivisions  of  the  Tertiary  as  now 
recognized  in  various  parts  of  the  United  States: 


TERTIARY  SYSTEM 

UPPER  TERTIARY 

LOWER  TERTIARY 

PKocene 

Afioce?ie 

O^'&ocene 

Eocene 

Chesapeake 

rd     03 

t:  « 

«l 

^ 

«J2 

^^ 

G       m      jvj 

2 

o 

e^- 

^     b    » 

•73  ^ 

^  ,  , 

rt         ^ 

0        OS       ^       "S 

K  ^ 

&.     >> 

11 

|s  | 

•a  s   &  1 

.0    ^    ja    Ii 

>H     oa     0     0 

O^H 

K     Ja 
1     I'll 

h-3         ^ 

^"8 

x_x 

"2  8 

o  ^ 

I| 

02 

3  § 

^  "§      ca^" 

2 

QJ             58  c3 

r 

1            $% 

I   IB 

0         0 

^O     P-t        O 

Ij 

O  0             X        03 

_o 

- 

f 

a 

S 

•jj 

d 

*"*            d 

,x 

1 

>c»      «      § 

Wester 

.2 

1! 

PQ      PH 

o      d       •  a? 
§|| 

j  1    5 

P4 

o> 

1 

SU 

.1 

"g.? 

0  G 

| 

0 

»§ 

O 

°          °3          >)         02 

d 

li 

F 

M            cd 
S           02 

|S       f| 

P-i     5     -S      s 

d     "S      o      21 

C3         03       M       .^ 
OJ      02      S      > 

a 

d    1 
^   s 

It  should  be  distinctly  understood  that  exact  correlations  of 
the  various  formations  in  these  widely  separated  regions  are  not 
meant  to  be  implied  in  the  above  table. 


THE  TERTIARY  PERIOD 


283 


DISTRIBUTION  AND  CHARACTER  OF  THE  ROCKS 

General  Distribution.  —  Lower  Tertiary  (Eocene  and  Oligo- 
cene)  strata  appear  at  the  surface  in  North  America  over  the  areas 
indicated  on  map  Fig.  175.  Disregarding  the  countries  south  of 


Fig.  175 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Lower  Tertiary 
(Eocene  and  Oligocene)  strata  in  North  America.  Tertiary  lavas  are 
separately  shown  on  map  figure  184.  (Modified  by  W.  J.  M.  after  Willis, 
U.  S.  Geological  Survey.) 


284  HISTORICAL  GEOLOGY 

the  United  States,  there  are,  in  general,  four  regions :  Atlantic  and 
Gulf  Coastal  Plain;  western  interior;  Pacific  Coast;  and  Alaska. 
The  discontinuity  of  the  areas  on  the  Atlantic  and  Gulf  Plain, 
especially  the  former,  is  due  to  the  fact  that  later  deposits  overlap 
and  conceal  the  Lower  Tertiary  strata  in  places.  The  Lower 
Tertiary  strata  extend  oceanward  or  Gulfward  under  much  or  all 
of  the  Coastal  Plain.  In  the  western  interior  the  numerous  dis- 
connected areas  are  chiefly  due  either  to  deposition  in  separate 
basins  or  removal  of  the  strata  from  some  places  by  erosion.  On 
the  Pacific  Coast,  Lower  Tertiary  strata  appear  mostly  as  small, 
narrow  belts,  because  only  the  eroded  edges  of  the  upturned  and 
folded  rocks  are  visible  in  the  mountains.  Such  strata  are  in  reality 
much  more  extensively  developed  than  these  surface  areas  seem  to 
indicate.  There  is  no  evidence  that  Lower  Tertiary  strata  were 
deposited  over  any  other  parts  of  the  continent  than  those  above 
mentioned. 

Upper  Tertiary  (Miocene  and  Pliocene)  strata  show  a  surface 
distribution  as  indicated  on  map  Fig.  176.  In  general  this  dis- 
tribution is  much  like  that  of  the  Lower  Tertiary.  On  the  Atlantic 
and  Gulf  Coastal  Plain,  it  is  quite  the  rule  that  the  Upper  Tertiary 
beds  form  a  somewhat  discontinuous  belt  between  the  continental 
margin  and  the  belt  of  Lower  Tertiary  beds.  Upper  Tertiary 
strata  are  more  extensive  at  the  surface  than  Lower  Tertiary  on 
the  Atlantic  Coast  and  less  extensive  on  the  Gulf  Coast.  The 
margin  of  the  continent,  as  well  as  much  of  Florida,  are  occupied 
by  Quaternary  deposits  which  are,  mostly  at  least,  underlain  by 
the  Upper  Tertiary.  In  the  western  interior  a  large,  nearly  continu- 
ous area  extends  from  northern  Texas  into  South  Dakota.  The 
comparatively  small,  disconnected  areas  in  the  northwestern 
United  States  mostly  represent  deposition  in  separate  basins. 
On  the  Pacific  border  of  the  United  States  the  Upper  Tertiary 
outcrops  extensively  as  long,  narrow  bands,  due  to  the  fact  that 
usually  only  the  edges  of  the  upturned  strata  are  exposed.  In 
British  Columbia  and  Alaska  Upper  Tertiary  rocks  are  only 
slightly  developed.  It  is  not  known  that  late  Tertiary  strata  ever 
occupied  any  other  portions  of  the  United  States  or  Canada  than 
those  above  mentioned. 

Atlantic  Coastal  Plain  Strata.  —  Lower  Tertiary  (Eocene) 
strata  are  only  slightly  exposed  to  view,  while  those  of  Upper 
Tertiary  (Miocene  and  Pliocene)  age  are  extensively  exposed  in  the 


THE  TERTIARY  PERIOD 


285 


Atlantic  Coastal  Plain.     All  the  formations,  except  possibly  the 
Lafayette,  are  there  of  marine  origin  and  usually  very  fossiliferous. 


Fig.  176 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Upper  Tertiary 
(Miocene  and  Pliocene)  strata  in  North  America.  (Modified  by  W.  J.  M. 
after  Willis,  U.  S.  Geological  Survey.) 

The  Eocene  formations  consist  very  largely  of  greensand  marls 
and  some  clays.  They  show  a  maximum  thickness  of  about  250 
feet  in  Maryland  and  rest  unconformably  upon  the  older  de- 


286 


HISTORICAL  GEOLOGY 


posits.  Oligocene  strata  have  not  been  recognized  north  of  South 
Carolina. 

The  Miocene  beds  are  well  developed,  with  a  maximum  thick- 
ness of  nearly  500  feet.  They  are  made  up  mostly  of  sands,  clays, 
and  marls. 

The  Pliocene  is  represented  by  the  marine  Waccamaw  forma- 
tion, which  consists  mostly  of  buff  sands  with  some  quartz  pebbles 


Fig.  177 

Eocene  sandstone  resting  by  sharp  contact  upon  Upper  Cretaceous  white 
chalk  in  Alabama.  (After  L.  W.  Stephenson,  U.  S.  Geological  Survey, 
Prof.  Paper  90- J.) 

and  shell  marls.  The  Pliocene  is  also  thought  to  be  represented 
by  the  problematical  Lafayette  formation  (see  below) ,  which  com- 
prises sands,  clays,  loams,  and  gravels  often  rich  in  iron  oxides. 
Its  thickness  seldom  exceeds  50  feet.  Lack  of  fossils  makes  it 
uncertain  whether  the  formation  is  late  Pliocene  or  early  Pleisto- 
cene in  age. 

Gulf  Coastal  Plain  Strata.  —  Here  the  Lower  Tertiary  (Eocene 
and  Oligocene)  strata  are  much  more  extensive  at  the  surface 
than  the  Upper  Tertiary.  Both  marine  and  non-marine  deposits 
are  present,  with  the  former  predominant. 


THE  TERTIARY  PERIOD  287 

The  Eocene  formations  are  much  thicker  (1700  feet  maximum) 
than  on  the  Atlantic  Coast.  Also  the  deposits  are  quite  distinctly 
hardened  into  sandstones,  shales,  and  limestones,  with  much  lig- 
nite in  some  places. 

The  Oligocene  is  well  represented  by  the  Vicksburg  limestone 
formation  and  the  Apalachicola  formation,  which  latter  is  very 
variable  but  mostly  made  up  of  limestones,  marls,  sands,  and  clays. 
These  two  formations  are  usually  only  a  few  hundred  feet  thick. 

Miocene  strata  are  represented  in  Florida  by  the  Jacksonville 
limestone  and  Choctawhatchee  marl,  in  the  Alabama  region  by  the 
Pascagoula  bluish  clay  formation,  and  in  Texas  by  the  Oakville 
limestone  formation.  A  maximum  thickness  of  fully  1500  feet  is 
attained  in  Texas. 

The  Pliocene  is  represented  in  Florida  by  the  marine  Caloosa- 
hatchee  marl  formation,  but  throughout  the  rest  of  the  Gulf  Coast 
the  Cilronelle  formation  appears  to  be  the  only  representative  of 
the  Pliocene. 

Western  Interior  Strata.  —  All  Tertiary  strata  of  the  western 
interior  are  of  non-marine  origin,  and  they  comprise  lake,  river, 
alluvial-fan,  and  wind  deposits,  with  some  volcanic  ash  and  tuff 
(Fig.  178). 

Of  the  Eocene  deposits,  the  Fort  Union  sands,  clays,  etc. 
(both  lacustrine  and  subaerial) ,  occur  in  North  Dakota,  Montana, 
and  southwestern  Canada,  where  they  reach  a  maximum  thickness 
of  2000  feet;  the  Wind  River  variegated  shales,  together  with 
some  sandstones  and  volcanic  ash,  are  terrestrial  (mostly  fluviatile) 
deposits  several  hundred  feet  thick  in  Wyoming;  the  Wasatch 
variegated  clays,  shales,  and  sandstones,  together  with  some  coal, 
are  very  largely  terrestrial  deposits  up  to  several  thousand  feet 
thick  in  Utah,  western  Colorado,  and  Wyoming;  the  Bridger  beds, 
many  hundreds  of  feet  thick,  are  mostly  volcanic  dust,  with  some 
shales,  etc.,  deposited  partly  on  land  and  partly  in  shallow  lakes 
in  western  Wyoming  and  northern  Utah,  while  the  San  Juan 
formation,  probably  of  the  same  age,  is  a  great  volcanic  tuff  deposit 
up  to  2000  feet  thick  in  Colorado;  the  Green  River  shales  are 
lacustrine  deposits  just  to  the  north  and  south  of  the  Uinta 
Mountains;  and  the  Uinta  shales,  sandstones,  etc.,  are  chiefly  of 
terrestrial  origin  in  western  Wyoming,  northeastern  Utah,  and 
northwestern  Colorado. 

Oligocene  strata,  represented  by  the  White  River  formation  of 


288 


HISTORICAL  GEOLOGY 


moderate  thickness,  occupy  extensive  areas  in  Wyoming,,  western 
South  Dakota,  western  Nebraska,  and  eastern  Colorado.  The 
formation  consists  of  clays  and  sandstones,  with  some  limestone  and 
volcanic  ash,  variously  deposited  in  lakes,  by  rivers,  by  wind,  etc. 
The  Miocene,  far  less  thick  than  the  Eocene,  is  represented 
toward  the  base  by  the  Arikaree  formation  of  chiefly  soft  sand- 


1 


Fig.  178 

Eocene-Oligocene  strata  as  seen  in  the  Wind  River 
Basin  of  Wyoming.  3,  Eocene  sandstone;  4,  5,  6,  7, 
Eocene  sandstone  and  shale;  8,  9,  Oligocene  volcanic 
dust  and  marl.  (After  Sinclair  and  Granger,  Amer. 
Mus.  Nat.  Hist.,  Bui.  30.) 

stones  some  hundreds  of  feet  thick  in  South  Dakota,  Nebraska, 
and  Wyoming;  toward  the  middle  by  the  Florissant  beds,  which 
consist  of  laminated  shales  formed  by  deposition  of  fine  volcanic 
ash  in  a  small  lake  in  Colorado  and  remarkable  for  the  great  num- 
ber of  insects  and  plants  contained  in  it;  and  toward  the  top  by 
the  Loup  Fork  beds,  which  form  thin  deposits  of  fine  sands  and 
marls  (both  subaerial  and  lacustrine)  over  extensive  areas  from 
South  Dakota  to  Mexico. 


THE  TERTIARY  PERIOD  289 

Pliocene  deposits  formed  in  many  parts  of  the  western  interior, 
but  for  most  part  they  are  difficult  to  separate  from  the  later 
(Pleistocene)  deposits.  They  are  mostly  of  terrestrial  origin, 
though  probably  with  some  lake  deposits.  Two  formations  which 
have  been  described  as  Pliocene  east  of  the  Rockies  are  the  Repub- 
lican River  of  Kansas  and  Nebraska,  and  the  Blanco  of  northern 
Texas  and  Nebraska.  Other  Pliocene  deposits  quite  certainly 
occur  west  of  the  main  axis  of  the  Rockies. 

In  addition  to  the  Tertiary  beds  above  described  in  the  western 
interior,  there  are  also  many  small  to  large  deposits,  especially  of 
Miocene  and  Pliocene  ages,  in  the  northwestern  United  States 
and  the  Great  Basin  between  the  Rocky  and  Cascade  Mountains 
(see  map  Fig.  176).  For  most  part  these  formations  have  not  been 
carefully  studied,  though  it  is  known  that  they  represent  all  types 
of  continental  deposits.  Perhaps  the  best  known  area  is  the  John 
Day  basin  of  eastern  Oregon,  where  various  continental  deposits, 
including  volcanic  ash,  attain  a  thickness  of  several  thousand  feet 
and  are  particularly  rich  in  Eocene  and  Oligocene  fossils. 

Pacific  Coast  Strata.  —  Tertiary  marine  strata,  together  with 
some  brackish  and  fresh  water  deposits,  are  extensively  developed 
west  of  the  Sierras  and  Cascades  and  along  the  southern  coast  of 
Alaska. 

Eocene  strata  are  prominently  developed  in  California,  Oregon, 
Washington,  and  Alaska.  They  are  mostly  of  marine  and  brackish 
water  origin  and  very  thick  (maximum  8000  to  12,000  feet). 
They  are  chiefly  sandstones  and  shales,  but  with  locally  developed 
tuffs,  conglomerates,  and  diatomaceous  shales.  Some  Eocene 
strata  of  Alaska  and  Washington  are  of  palustrine  origin  and 
contain  coal. 

Oligocene  strata  are  much  less  widely  distributed  than  the 
Eocene.  The  deposits  are  mostly  sandstones  and  shales  of  marine 
origin  in  western  Washington  and  Oregon,  and  north  of  Los 
Angeles  in  California.  Similar  beds  are  known  on  the  Alaskan 
coast. 

Miocene  marine  strata  are  almost  as  prominently  represented 
on  the  Pacific  Coast  as  the  Eocene,  the  beds  being  very  largely 
sandstones  and  shales,  often  with  much  diatomaceous  earth  or 
shale,  especially  in  the  Monterey  formation  (Fig.  179).  The 
Miocene  strata  exhibit  a  maximum  thickness  of  from  14,000  to 
16,000  feet,  the  Monterey  alone  reaching  a  thickness  of  5000  feet. 


290 


HISTORICAL  GEOLOGY 


Pliocene  marine  strata  are  far  less  extensively  developed  on  the 
Pacific  Coast  than  the  Miocene,  the  principal  areas  being  in  the 
Coast  Ranges  of  California,  and  two  or  three  small  areas  on 
the  coast  of  Oregon.  Pliocene  fresh  water  beds  are  widely  devel- 
oped in  the  southern  half  of  the  Great  Valley  of  California.  The 


Fig.  179 

Soft  white  diatomaceous  Miocene  shale  in  southern  California.    (After  Arnold, 
U.  S.  Geological  Survey,  Bui.  322.) 

maximum  thickness  of  the  marine  Pliocene  is  at  least  4000  to  5000 
feet  to  the  south  of  San  Francisco. 

Thickness  of  the  Tertiary.  —  In  the  above  descriptions  some 
details  have  been  given  regarding  the  thickness  of  Tertiary  for- 
mations. To  summarize  for  the  whole  Tertiary,  the  maximum 
thickness  of  the  whole  system  (not  including  igneous  rocks)  on  the 
Atlantic  Coast  is  less  than  1000  feet;  on  the  western  Gulf  Coast 
between  3000  and  4000  feet;  in  the  western  interior  many  thou- 
sands of  feet,  though  usually  not  more  than  a  few  thousand  feet 
occur  in  any  one  locality,  because  in  no  case  are  all  the  formations 


THE  TERTIARY  PERIOD  291 

present;  and  on  the  Pacific  Coast  fully  30,000  feet,  with  a  thick- 
ness of  10,000  to  20,000  feet  shown  in  many  districts.  According  to 
these  figures  it  is  seen  that  the  thickness  of  the  Tertiary  system 
is  quite  comparable  to  that  of  ordinary  Paleozoic  or  Mesozoic 
systems. 

Igneous  Rocks.  —  In  the  above  descriptions,  attention  has 
been  wholly  given  to  a  consideration  of  the  sedimentary  rocks 
(including  some  tuffs  and  volcanic  ash  deposits),  but  the  igneous 
rocks  of  Tertiary  age  are  also  of  very  great  extent  and  importance, 
particularly  in  the  northwestern  part  of  the  United  States.  This 
igneous  activity  will  be  discussed  below  in  connection  with  the 
Tertiary  physical  history  of  North  America. 

PHYSICAL  HISTORY 

In  the  interest  of  more  clearly  presenting  an  outline  of  our 
unusually  detailed  knowledge  of  the  complicated  physical  history 
of  this  comparatively  recent  (Tertiary)  period,  we  shall  depart 
slightly  from  our  ordinary  method  by  considering  first  the  relations 
of  land  and  water,  basins  of  deposition  and  character  of  sediments 
in  different  parts  of  the  continent,  etc.,  after  which  will  follow  a 
discussion  of  the  development  of  relief  features  in  the  east  and  west, 
and  mountain  making  and  igneous  activity  in  the  west. 

Atlantic  Coast.  —  During  most  of  the  time  from  Eocene  to 
Miocene  inclusive,  much  of  the  Atlantic  Coastal  plain  (including 
Florida)  was  occupied  by  marine  water  (see  Figs.  180, 181).  Certain 
unconformities,  especially  between  the  Eocene  and  Miocene,  show 
that  there  were  some  retrogressions  and  transgressions  of  the  sea. 
During  Eocene  time  the  newly  added  belt  of  Cretaceous  deposits 
lay  along  the  shore,  and  the  Eocene  strata  are  known  to  have  been 
mostly  derived  from  the  Cretaceous  and  in  part  from  the  more 
inland  older  formations.  In  general,  it  may  be  said  that,  to  and 
including  the  Miocene,  there  was  a  tendency  to  gradually  push 
the  shore  line  farther  eastward  by  the  addition  of  strips  of  land. 

With  the  possible  exception  of  the  Lafayette,  which  is  usually 
regarded  as  of  Pliocene  age,  the  only  marine  strata  of  Pliocene  age 
comprise  the  comparatively  thin  Waccamaw  formation  on  the 
middle  Atlantic  Coast. 

The  Lafayette  deposits  of  North  Carolina,  according  to  Ste- 
phenson  and  Johnson,  "are  present  as  surficial  coverings  (10  to  40 


292  HISTORICAL  GEOLOGY 

miles  wide),  probably  at  but  few  places  exceeding  25  or  30  feet 
in  thickness,  along  the  northwestern  border  of  the  Coastal  Plain 
province.  They  occur  for  the  most  part  at  elevations  of  from  200 
to  500  feet  and  form  mouth-like  coverings  which  cap  the  tops  of, 
and  lap  down  over  the  slopes  of,  the  pre-Lafayette  hills.  The 
materials  consist  of  sandy  loams  and  sands,  as  a  rule  coarse  and  in 
places  arkosic,  and  having  at  their  base  at  many  places  a  bed  of 
coarse  gravel  and  cobbles."  *  In  Maryland  the  Lafayette  is  quite 
distinctly  terrace-like.  According  to  one  view  it  is  of  continental 
origin  and  was  deposited  as  a  result  of  "a  comparatively  rapid 
Pliocene  uplift  in  the  Appalachian  region"  (W.  H.  Ball),  which, 
early  in  the  Pliocene,  had  become  mantled  with  deep  residual  soil 
so  that  the  revived  streams  picked  up  and  carried  great  loads  of 
debris  which  were  spread  over  the  relatively  flat  lands  near  sea 
level.  Another  explanation  is  that  the  I^afayette  was  of  marine 
origin,  due  to  simultaneous  depression  of  the  Coastal  Plain  district 
and  elevation  of  the  Piedmont  Plateau  and  Appalachian  areas 
when  "streams  gorged  with  detritus  from  the  decayed,  uplifted 
Piedmont  above  rushed  down  to  the  sea  and  poured  their  contents 
into  the  ocean"  (G.  B.  Shattuck).  The  most  likely  view  is  that  the 
Lafayette  is  a  normal  marine  terrace,  much  like  the  later  ones 
below  described,  and  that,  "with  the  successive  oscillations  of  the 
coast  line,  terraces  have  been  formed  at  levels  where  the  sea  has 
stood  for  any  considerable  period  of  time"  (W.  B.  Clark).  Careful 
search  has  failed  to  produce  any  marine  fossils  from  the  formation. 

Gulf  Coast.  —  During  Eocene-Oligocene  time  extensive  sedi- 
mentation, both  marine  and  non-marine,  took  place  over  the  Gulf 
Coastal  Plain  area.  The  Mississippian  embayment  (see  Fig.  180) 
extended  northward  (to  the  mouth  of  the  Ohio  River)  as  it  did  in 
the  Cretaceous,  and  the  unconformity  between  the  Cretaceous 
and  Eocene  clearly  shows  a  transgression  of  the  sea  over  the  area 
in  Eocene  time.  Marine  conditions  in  this  embayment  were, 
however,  more  or  less  interrupted  as  proved  by  the  considerable 
development  of  non-marine  deposits  such  as  lignite  beds.  Over 
.  Florida,  the  Gulf  Coast  of  Mexico,  and  much  of  the  coast  of  Texas, 
true  marine  deposition  went  on  during  practically  all  of  Eocene 
and  Oligocene  times. 

During  Miocene  time  the  Mississippi  embayment  was  greatly 

1  The  Coastal  Plain  of  North  Carolina:  North  Carolina  Geological  and 
Economic  Survey,  1912,  p.  359. 


THE  TERTIARY  PERIOD 


293 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAI.) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA.  MORE  LIKELY  LAKD 
LANDS 
INDETERMINATE  AREAS 

POLAR 


CONTINENTAL  DEPOSITS.  SOMETIMES 
INCLUDING  MARINE  SEDIMENTS 


Fig.  180 

Paleogeographic  map  of  North  America  during  Lower  Tertiary  (Eocene- 
Oligocene)  time.  (Slightly  modified  after  Bailey  Willis,  courtesy  of  The 
Journal  of  Geology.} 


294  HISTORICAL  GEOLOGY 

restricted,  but  marine  waters  spread  over  the  whole  Gulf  Coast 
from  Florida  to  southern  Mexico,  except  for  a  small  island  in 
Florida  (see  Fig.  181). 

The  presence  of  some  marine  Pliocene  strata  in  Florida  and 
along  the  Gulf  Coastal  Plain  border  shows  those  areas  to  have 
been  submerged  during  portions  of  Pliocene  time  at  least. 

Western  Interior.  —  The  extensive  folding,  faulting,  and  lava 
extrusions  which  marked  the  close  of  the  Cretaceous  period  left 
the  western  interior  topographically  rugged  with  conditions 
favorable  for  rapid  erosion  of  the  mountains  and  deposition  of 
sediments  in  the  intermontane  basins.  As  the  character  of  the 
Tertiary  sediments  indicates,  all  sorts  of  continental  deposits  were 
formed,  that  is  in  lakes,  on  river  flood-plains,  as  alluvial  fans,  as 
wind-blown  deposits,  and  even  as  volcanic  dust  or  tuff  in  many 
places.  Marine  deposition  was  wholly  lacking.  As  shown  by  the 
above  statements  regarding  the  distribution  of  the  various  forma- 
tions, it  is  apparent  that  the  principal  areas  over  which  sediments 
were  being  deposited  must  have  shifted  more  or  less. 

That  there  was  very  active  vulcanism  during  Tertiary  time  in 
this  western  interior  region  is  proved  by  the  presence  of  so  much 
volcanic  dust  and  ash.  Also  in  the  great  area  between  the  Rockies 
and  Sierra-Cascade  Ranges,  there  was  tremendous  volcanic  activ- 
ity, but  this  will  be  described  under  a  separate  heading  below. 

Many  of  the  Tertiary  deposits  of  the  western  interior  now  lie 
at  altitudes  of  from  5000  to  10,000  feet  above  the  sea,  and  they 
have  been  somewhat  deformed  by  tilting  or  warping. 

Pacific  Coast.  —  Summarizing  the  physical  history  of  the  Pa- 
cific Coast  during  Cenozoic  time,  Ralph  Arnold  says  in  part: 
"Following  the  period  of  elevation  and  erosion  at  the  close  of  the 
Cretaceous,  the  Eocene  was  inaugurated  by  a  subsidence  below 
sea-level  of  the  greater  part  of  western  Washington  and  Oregon 
and  the  western  part  of  central  and  southern  California.  Volcanic 
activity  was  pronounced  in  the  early  and  middle  Eocene.  Later 
in  the  Eocene  brackish  and  freshwater  conditions  prevailed  over 
the  same  area,  and  extended  over  much  of  Alaska.  .  .  .  The 
Oligocene  was  a  period  of  elevation,  with  marine  conditions  re- 
stricted to  a  much  smaller  area  than  in  the  Eocene.  .  .  .  The 
lower  Miocene  marked  a  widespread  subsidence  in  the  Coastal  belt 
which  was  followed  by  a  period  of  mountain  building  (Coast 
Ranges)  and  great  local  deformation,  vulcanism,  etc.  .  .  .  The 


THE  TERTIARY  PERIOD 


295 


LEGEND 

OCEANIC  BASINS 
MARINE  WATERS  (EPICONTINENTAL) 
SEA  OR  LAND.  MORE  LIKELY  SEA 
LAND  OR  SEA,  MORE  LIKELY  LAND 
LANDS 
TEMPORARY   LAND 

POLAR 


CONTINENTAL  DEPOSITS,  SOMETIM 
INCLUDING  MARINE  SEDIMENTS 


Fig.  181 

Paleogeographic  map  of  North  America  during  Miocene  time.      (Slightly 
modified  after  Bailey  Willis,  courtesy  of  The  Journal  of  Geology.} 


296 


HISTORICAL  GEOLOGY 


upper  Miocene  was  a  period  of  subsidence,  with  ideal  conditions 
for  maximum  deposition  of  sediments  in  local  basins.  During 
Pliocene  and  early  Pleistocene  time  there  was  a  continuation  of 
many  of  the  upper  Miocene  conditions,  except  that  marine  en- 
vironment gave  way  to  freshwater.  ...  A  period  of  elevation 


Fig.  182 

"Toadstool  Park":  a  view  in  the  Bad  Lands  of  western  Nebraska.  The 
rocks  are  of  Oligocene  age.  (After  Darton,  U.  S.  Geological  Survey,  Prof. 
Paper  17.) 

and    considerable    local    deformation    in    the    early    Pleistocene 
inaugurated  the  present  conditions  on  the  Pacific  Coast."  1 

Development  of  Relief  Features  in  the  Eastern  United 
States.  —  The  uplift  of  the  great  Cretaceous  peneplain  was  an 
event  of  prime  importance  for  the  eastern  United  States,  because 
it  literally  furnishes  us  with  the  beginning  of  the  history  of  most  of 
the  existing  relief  features  of  the  Appalachian  district  as  well  as 

1  Ralph  Arnold:  Outlines  of  Geologic  History,  by  Willis  and  Salisbury, 
p.  248. 


THE  TERTIARY   PERIOD 


297 


>     P-j 

?P 


New  York  and  much  of  New  England.  Hence  we  assert,  with 
emphasis,  that  all  the  principal  topographic  features  of  this  region 
as  we  see  them  today  date  from  the  uplift  of  the  Cretaceous 
peneplain,  because  they  have  been  produced  by  the  dissection  of 
that  upraised  surface.  This  dissec- 
tion was  largely  the  work  of  erosion, 
though  more  locally  (e.g.  the  eastern 
Adirondack  Mountains)  faulting  has 
produced  notable  effects.  All  the 
valleys,  great  and  small,  such  as  the 
Champlain,  Connecticut,  Mohawk, 
Hudson,  the  Great  Lakes  valleys, 
and  the  valleys  of  the  Appalachians, 
have  been  produced  since  the  uplift 
of  the  peneplain. 

The  uplift  greatly  revived  the 
activity  of  the  streams,  so  that  they 
became  very  active  agents  of  ero- 
sion, first  cutting  channels  through 
the  alluvial  deposits,  and  then  into 
the  underlying  bed  rock.  Thus 
these  large  original  streams  had 
their  courses  determined  in  the  over- 
lying deposits,  and  when  the  un- 
derlying rocks  were  reached  the 
same  courses  had  to  be  pursued 
entirely  without  reference  to  the 
underlying  rock  character  and  struc- 
ture. Fine  examples  of  such  (super- 
imposed) streams,  which  are  now 
entirely  out  of  harmony  with  the 
structure  of  the  regions  through 
which  they  flow  are  the  Susque- 
hanna,  Delaware,  and  Hudson. 
Thus  the  Susquehanna  cuts  across 
a  whole  succession  of  Appalachian 
ridges,  while,  in  accordance  with  the  same  explanation,  the 
Delaware  cuts  through  the  Kittatinny  ridge  at  the  famous  Dela- 
ware Water  Gap.  The  lowei  Hudson  pursues  a  course  no  less  out 
of  harmony  with  the  country  through  which  it  passes.  It  flows  at 


p.  -2:1 


ST.  W     3 
OB    <&    D 


298  HISTORICAL  GEOLOGY 

a  considerable  angle  across  the  old  Taconic  folds  above  the  High- 
lands, after  which  it  passes  through  a  deep  gorge  which  it  has  cut 
through  the  hard  granites  and  other  rocks  of  the  Highlands.  The 
simple  explanation  is  that  the  Hudson  had  its  course  determined 
upon  the  surface  of  the  upraised  Cretaceous  peneplain,  and  that 
it  has  been  able  to  keep  that  course  in  spite  of  the  discordant  struc- 
tures of  the  underlying  rocks.  The  seemingly  anomalous  courses 
of  the  Delaware,  Potomac,  Susquehanna,  etc.,  are  to  be  similarly 
explained. 

But  while  the  great  master  streams  were  thus  cutting  deep 
trenches  in  hard  and  soft  rock  alike,  numerous  side  streams  or 
tributaries  came  into  existence  and  naturally  developed  along  the 
belts  of  weak  rock  and  in  harmony  with  the  geologic  structures. 
This  principle  is  especially  well  illustrated  by  all  of  the  streams 
now  occupying  the  valleys  between  the  Appalachian  ridges. 

After  the  uplift  of  the  peneplain,  the  larger  streams  cut  down 
their  channels  most  rapidly  and  were  the  first  to  reach  " grade," 
that  is  a  condition  in  which,  because  of  low  velocity,  they  could  no 
longer  cut  down  their  channels,  though  the  widening  process  could 
continue  because  of  side  cutting  due  to  meandering  of  the  streams 
back  and  forth  from  one  side  to  the  other  of  the  channels.  The 
commonly  occurring,  deep,  broad-bottomed,  stream-cut  valleys,  in 
the  area  under  discussion,  show  that  many  of  the  streams  had 
reached  graded,  or  nearly  graded,  condition  even  by  the  close  of  the 
Tertiary.  In  the  northern  Appalachian  district,  at  least,  we  have 
evidence  to  show  that  after  the  streams  had  reached  grade  there 
was  an  appreciable  renewed  uplift  of  the  land  which  again  revived 
the  activity  of  the  streams.  Thus  the  broad  Hudson  Valley,  with 
minor  hills  rising  above  its  surface,  was  produced  when  the  Hudson 
was  well  along  toward  a  graded  condition  and  then,  as  a  result  of 
this  late  Tertiary  uplift  of  the  land,  the  present  narrow  and  fairly 
deep  inner-  channel  of  the  Hudson  was  formed.  The  Hudson  did 
not  reach  grade  in  this  inner  channel,  its  work  having  been  inter- 
rupted by  both  the  subsidence  of  the  land  and  the  spreading  of 
the  great  ice  sheet  over  the  region. 

This  -inner  channel  of  the  Hudson  has  been  traced  for  fully  100 
miles  eastward  beyond  the  mouth  of  the  present  river.  The 
Coast  and  Geodetic  Survey  has  made  a  detailed  map  of  the 
ocean  bottom  near  New  York  City,  and  the  submerged  chan- 
nel of  the  Hudson  River  is  clearly  shown  as  a  distinct  trench 


THE  TERTIARY  PERIOD  299 

cut  into  the  continental  shelf.  Even  in  the  Hudson  Valley  above 
New  York  City,  the  narrow  inner  rock  channel  has  a  depth  of 
hundreds  of  feet  and  is  mostly  submerged  below  tide  water. 
Without  question,  this  submerged  Hudson  channel  was  cut  when 
the  region  was  dry  land,  and  thus  we  have  positive  proof  that, 
late  in  the  Tertiary  and  possibly  extending  into  the  early  Quater- 
nary, the  region  of  southeastern  New  York  was  notably  higher 
than  it  is  today.  Conservative  estimates  place  the  amount  of 
elevation  greater  then  than  now  at  not  less  than  2000  feet  because 
the  end  of  the  Hudson  channel  is  submerged  to  that  extent.1  The 
coast  was  then  at  what  is  now  the  edge  of  the  continental  shelf  or 
platform  about  100  miles  east  of  the  present  coast  line.  That  this 
greater  altitude  was  before  the  Ice  age  is  proved  by  the  fact  that 
the  inner  Hudson  channel  now  contains  much  glacial  debris 
filling. 

By  similar  reasoning,  based  upon  the  drowned  valleys  of  the 
Maine  coast  and  the  lower  St.  Lawrence,  we  know  that  all  of  the 
middle  Atlantic  sea-board  region,  at  least,  was  notably  higher  in 
late  Tertiary  time  than  now. 

The  Mississippi  Valley  area  also  appears  to  have  been  notably 
elevated  during  late  Tertiary  time,  and  hence  the  major  (erosion) 
relief  features  of  that  great  area,  as  we  now  know  them,  have  been 
produced  by  the  dissection  of  that  upraised  area  by  streams. 

Mountain  Making  and  Development  of  Relief  in  the  West.2  — 
In  North  America,  as  well  as  other  continents,  the  Tertiary  was  a 
period  of  unusual  mountain-making  activity.  Many  of  the  present 
great  mountain  ranges  of  the  earth  actually  had  their  birth  and 
principal  development  during  this  period,  while  others  were  re- 
juvenated and  brought  essentially  to  their  present  form  and 
altitudes. 

Coast  Ranges.  —  This  belt  was  somewhat  affected  by  deforma- 
tive  movements  toward  the  close  of  the  Jurassic,  as  we  have  already 

1  It  has  been  suggested  by  Chamberlin  and  Salisbury  (Geology,  Vol.  1, 
p.  529)  that  the  very  end  of  the  Hudson,  and  other  submerged  channels, 
may  have  been  deepened  by  tidal  scouring  and,  if  so,  the  figure  (2000  feet) 
generally  given  may  be  too  high.     At  any  rate  the  Hudson  channel  at  the 
Highlands  is  submerged  nearly  800  feet,  which  certainly  implies  an  altitude 
of  more  than  1000  feet  greater  than  now  when  the  river  was  there  actively 
eroding. 

2  The  topographic  influence  of  Tertiary  vulcanism  in  the  west  will  be 
described  under  another  heading. 


300  HISTORICAL  GEOLOGY 

seen,  but  probably  not  more  than  a  chain  of  islands  was  then 
developed.  Another  time  of  moderate  elevation  occurred  during  the 
Eocene.  The  Oligocene  was  a  time  of  considerable  elevation  and 
erosion  in  the  Coast  Range  district,  though  the  relief  could  not 
have  been  strong,  as  shown  by  the  fine-grained  sediment  which  was 
deposited  during  the  Oligocene  in  the  limited  areas  of  southern 
California  and  western  Oregon  and  Washington. 

What  may  really  be  called  the  "Coast  Range  Revolution" 
took  place  in  mid-Miocene  time.  According  to  Arnold,  "one  of  the 
most  widespread  and  important  periods  of  diastrophism  in  the 
Tertiary  history  of  the  Pacific  Coast  was  that  immediately  follow- 
ing the  deposition  of  the  Monterey  or  lower  middle  Miocene.  Its 
effects  are  visible  from  Puget  Sound  to  southern  California.  It  is 
marked  as  much  by  readjustment,  by  local  faulting  and  folding, 
as  by  general  movements  of  elevation  and  subsidence.  In  some 
regions  the  folding  and  faulting  were  intense,  the  greatest  dis- 
turbance accompanying  the  uplift  of  the  mountain  ranges  to  an 
altitude  of  thousands  of  feet  (Fig.  183).  In  other  regions  low 
broad  folds  were  formed  during  the  post-Miocene  disturbance,  and 
the  strata  were  not  upheaved  to  a  great  altitude.  Faulting  on  ,a 
most  magnificent  scale  took  place  along  the  (San  Francisco)  earth- 
quake rift  (fault)  and  certain  other  fault-zones.  .  .  .  The  post- 
Monterey  diastrophic  movements  in  the  Puget  Sound  province 
also  produced  sharp  relief,  as  is  evidenced  by  the  coarse  sediments 
deposited  immediately  following  the  disturbance."  1 

Other  important  mountain-making  movements  took  place 
during  the  Quaternary,  with  minor  activity  continuing  to  the 
present  time.  The  combination  of  the  various  diastrophic  move- 
ments and  erosion  in  the  Coast  Range  belt  since  early  Tertiary 
time  has  given  rise  to  the  Pacific  border  mountains  as  we  see  them 
today. 

Sierra  Nevada  and  Cascade  Ranges.  —  We  have  already  seen 
that  the  Sierras  were  produced  by  crustal  disturbance  toward  the 
close  of  the  Jurassic  period.  From  that  time  till  late  in  the  Miocene 
epoch  the  mountain  mass  had  undergone  profound  erosion,  so  that 
it  was  reduced  to  a  range  of  hills  or  low  mountains  with  no  great 
relief  features.  In  other  words,  it  approached  the  condition  of  a 
peneplain.  Then,  late  in  the  Miocene  or  early  in  the  Pliocene, 

1  Ralph  Arnold:  Outlines  of  Geologic  History,  by  Willis  and  Salisbury, 
p.  242. 


THE  TERTIARY  PERIOD  301 

there  began  a  tremendous  rejuvenation  of  the  range,  caused  by 
the  development  of  profound  faulting  along  the  eastern  side.  The 
vast  earth-block  was  tilted  westward  with  steep  eastern  front  and 
long  gradual  slope  toward  the  west,  with  the  crest  of  the  block 
forming  the  summit  of  the  range.  The  maximum  amount  of  dis- 
placement along  this  fault  zone  is  no  less  than  15,000  feet  and,  in 
spite  of  subsequent  erosion,  the  fault-scarp  still  stands  out  as  a 
topographic  feature  usually  several  thousand  feet  high.  That  the 
faulting  has  not  yet  ceased  is  evidenced  by  the  Inyo  earthquake 
of  1872,  when  a  renewed  displacement  of  10  to  25  feet  took  place 
along  the  fault  zone  for  many  miles.  The  mighty  canyons  (e.g. 
Yosemite)  and  other  relief  features  of  the  Sierras  as  we  know  them 
today  have  been  sculptured  out  of  the  great  tilted  earth-block  by 
weathering  and  erosion. 

The  Cascade  Mountains,  too,  appear  to  have  approached  the 
peneplain  condition  by  late  Tertiary  time,  when  a  vigorous  re- 
juvenation took  place  by  an  arching  or  bowing  of  the  surface 
rather  than  by  profound  faulting. 

Great  Basin  and  Colorado  Plateau.  —  About  the  same  time 
(later  Tertiary)  the  whole  Great  Basin  region  between  the  Sierras 
and  the  Wasatch  Mountains  of  Utah  was  also  notably  affected  by 
faulting.  The  steep  western  front  of  the  Wasatch  represents  a 
profound  fault,  while  many  of  the  north-south  Basin  Ranges  of 
Nevada  are  tilted  earth-blocks. 

The  Cenozoic  history  of  the  Colorado  Plateau  region  still  pre- 
sents important  problems  for  future  studies.  According  to  Button 
the  Plateau  was  raised,  more  or  less  periodically,  fully  20,000  feet 
during  Tertiary  time,  but  its  surface  now  shows  an  altitude  of 
only  7000  to  8000  feet,  because  of  deep  erosion  during  its  uplift. 
As  a  result  of  the  rejuvenation  of  this  region,  the  Colorado  River 
was  very  actively  revived  and  has  carved  out  the  Grand  Canyon 
since  the  early  Tertiary.  Later  investigations,  however,  seem  to 
show  that  the  rejuvenation  was  much  later,  probably  late  Pliocene, 
and  that  most,  if  not  all  of  the  Grand  Canyon,  is  of  post-Tertiary 
age. 

Rocky  Mountain  and  Western  Interior  Regions.  —  Late  in  the 
Tertiary  much  of  the  Rocky  Mountain  region  was  also  greatly 
rejuvenated  by  an  uplift  or  upwarp,  unaccompanied  by  folding  of 
the  strata.  That  this  upwarp  amounted  to  some  thousand  of  feet 
is  distinctly  proved  by  the  fact  that  the  Miocene  beds  east  of  the 


302 


HISTORICAL  GEOLOGY 


Rockies  are  so  tilted  that  they  are  3000  feet  higher  close  to  the 
mountains  than  they  are  farther  east.    Also  the  fact  that  many 


A- 


L* 


m 


Fig.  184 

Map  showing  the  surface  distribution  (areas  of  outcrops)  of  Tertiary  and  later 
volcanic  rocks  in  North  America.  (Modified  by  W.  J.  M.  after  Willis, 
U.  S.  Geological  Survey.) 

large  areas  of  Tertiary  deposits  now  lie  from  5000  to  even  10,000 
feet  above  sea-level,  pretty  clearly  indicate  notable  elevation  since 
their  deposition,  because  such  deposits  must  have  been  formed  in 


THE  TERTIARY  PERIOD 

intermontane   basins   much    nearer   sea- 
level,  like  the  recent  deposits  of  the  Great     ^  2, 
Valley  of  California.  *  | 

The  dissection  by  erosion  of  the  usu-  ^  g 
ally  comparatively  soft  and  only  moder-  |.  ^ 
ately  tilted  deposits  of  Tertiary  age  in  the  ^  ^ 
western  interior  has  given  rise  to  much  of 
the  "Bad  Lands"  country,  so  called  be-  g ;  P 
cause  of  the  difficulty  early  explorers  had  5'  ^ 
in  travelling  across  that  rugged  region  ^J 
(Fig.  182).  2-g 

Igneous  Activity. — In  connection  with  5-  8 
the  discussion  of  the  close  of  the  Creta-  E£  ° 
ceous  period,  we  spoke  of  the  inaugura-  i,  | 
tion  of  igneous  activity  which  resulted  in  <  | 
the  building  up  of  the  vast  lava  plateau, 
occupying  fully  200,000  square  miles,  be-  '£>"• 
tween  western  Wyoming  (including  Yel-  J^ 
lowstone  Park)  and  the  Cascades  and 
southward  into  northern  Nevada  and 
northeastern  California  (Fig.  184).  Most 
of  this  lava  was  poured  out  in  Tertiary 
time,  particularly  in  the  latter  part. 
Norton  has  clearly  and  concisely  stated 
the  principal  facts  as  follows:  "For  thou- 
sands of  square  miles  the  surface  is  a  lava 
plain  which  meets  the  boundary  moun- 
tains as  a  lake  or  sea  meets  a  rugged  and 
deeply  indented  coast.  .  .  .  The  rivers 
which  drain  the  plateau  —  the  Snake,  the 
Columbia,  and  their  tributaries  —  have 
deeply  trenched  it,  yet  their  canyons, 
which  reach  the  depth  of  several  thou- 
sand feet,  have  not  been  worn  to  the  base 
of  the  lava  except  near  the  margin  and 
where  they  cut  the  summits  of  mountains 
drowned  beneath  the  flood.  Here  and 
there  the  plateau  has  been  deformed.  .  .  . 
The  plateau  has  been  built  like  that  of 
Iceland,  of  innumerable  overlapping  sheets 


304 


HISTORICAL  GEOLOGY 


of  lava  (Fig.  185).  .  .  .  The  average  thickness  of  flows  seems  to 
be  about  seventy-five  feet. 

"The  plateau  was  long  in  building.  Between  the  layers  are 
found  in  places  old  soil  beds  and  forest  grounds  and  the  sediments 
of  lakes.  ...  So  ancient  are  the  latest  floods  in  the  Columbia 
Basin  that  they  have  weathered  to  a  residual  yellow  clay  from 

thirty  to  sixty  feet  in  depth 
and  marvelously  rich  in  the 
mineral  substances  on  which 
plants  feed.  In  the  Snake 
River  Valley  the  latest  lavas 
are  much  younger.  Their  sur- 
faces are  so  fresh  and  un- 
decayed  that  here  the  effusive 
eruptions  may  have  continued 
to  within  the  period  of  hu- 
man history."  1 

Volcanic  activity  must 
have  been  very  pronounced 
along  the  Rockies  during  the 
Tertiary,  as  shown  by  exten- 
sive and  often  very  thick  de- 
posits of  tuff  or  volcanic  ash 
(e.g.  San  Juan  and  Florissant 
formations) .  Many  volcanoes 
also  broke  forth  on  the  Col- 
orado Plateau  of  Utah,  New 
Mexico,  and  Arizona,  in  the 
latter  state  especially  there 
being  cones  exhibiting  all 
stages  of  denudation  from 
very  recent  cinder  cones  to  others  where  only  the  merest  rem- 
nants or  "volcanic  necks"  are  left. 

In  the  northern  Coast  Range  mountains  of  the  United  States 
there  was  considerable  volcanic  activity  in  the  Eocene  and  much 
throughout  the  Range  in  the  Miocene. 

Very  pronounced  vulcanism  occurred  in  the  Cascade  Moun- 
tain region  during  the  Eocene  and  to  the  middle  Miocene.    During 
Pliocene  time  there  was  great  volcanic  activity  with  outpourings 
1  W.  H.  Norton:  Elements  of  Geology,  pp.  400-401. 


Fig.  186 

Mount  Lassen  in  northern  California 
in  eruption  August  22,  1914.  Smoke 
and  volcanic  ash  rose  to  a  height  of 
10,000  feet.  (From  a  photograph  by 
Restinson,  Red  Bluff,  Cal.) 


THE  TERTIARY  PERIOD  305 

of  lava  in  the  Sierras  and  Cascades.  At  that  time  the  Miocene 
gold-bearing  stream  gravels  of  California  were  buried  under  the 
lava.  Many  well-known  volcanic  mountains,  such  as  Shasta, 
Hood,  Rainier,  etc.,  date  from  that  time.  In  fact  this  period  of 
vulcanism  has  not  altogether  ceased  at  the  present  day,  as  shown 
by  a  renewal  of  activity  of  Lassen  Peak  (altitude  10,437  feet)  in 
northern  California  on  May  30,  1914.  At  the  present  writing 
(October,  1915)  there  have  been  about  150  eruptions  of  the  moun- 
tain, in  all  cases  fragmental  materials  only  having  been  ejected 
sometimes  to  a  height  of  5000  to  10,000  feet  above  the  mountain 
(Fig.  186).  The  eruptions  of  cinders  and  lava  at  Cinder  Cone, 
only  10  miles  from  Lassen  Peak,  occurred  not  over  200  years  ago. 
Other  quite  recent  cinder  cones  are  known  in  southern  California 
and  Arizona. 

FOREIGN  TERTIARY 

Eocene.  —  Just  after  the  emergence  of  much  of  Europe  at  the 
close  of  the  Mesozoic,  there  were  certain  basins  of  deposition  such 
as  lakes,  estuaries,  etc.  Early  in  the  Eocene,  however,  a  great 
submergence  set  in,  allowing  marine  waters  to  spread  over  a  con- 
siderable part  of  western  and  much  of  southern  Europe.  The 
southeastern  British  Isles,  the  northern  border  of  France,  Belgium, 
Holland,  the  northern  border  of  Germany,  the  site  of  the  Pyrenees, 
Italy,  all  but  the  axis  of  the  Alps,  much  of  southeastern  Europe, 
and  northern  Africa  were  submerged  (see  Fig.  187) .  This  greatly 
expanded  mediterranean  of  Europe  also  extended  eastward  across 
southwestern  Asia,  except  southern  Arabia  and  southern  India, 
to  connect  with  the  Indian  Ocean  through  the  Bay  of  Bengal. 
A  narrow  sound  along  the  eastern  side  of  the  Urals  connected 
this  mediterranean  with  the  Arctic.  In  this  vastly  expanded  in- 
terior sea  true  marine  deposition  took  place,  the  most  character- 
istic formation  being  known  as  Nummulitic  limestone,  so  called 
because  it  is  chiefly  made  up  of  shells  of  a  certain  species  (Num- 
mulites)  of  unusually  large  Foraminifers.  Perhaps  no  other 
single  formation  in  the  crust  of  the  earth  built  up  essentially  of 
the  remains  of  but  one  species  of  organism  is  so  widespread  and 
thick,  its  thickness  at  times  reaching  several  thousand  feet.  This 
marine  Nummulitic  limestone  now  occurs  at  altitudes  of  10,000 
feet  in  the  Alps,  and  fully  20,000  feet  in  Thibet.  Limestone  of 
this  age  was  quarried  for  the  building  of  the  Egyptian  pyramids. 


306 


HISTORICAL  GEOLOGY 


During  Eocene  time  also  the  island  region  along  the  eastern 
coast  of  Asia  was  largely  submerged  as  well  as  the  eastern  coasts 
of  Australia  and  South  America  (in  Argentina  and  Brazil).  Land 
seems  to  have  been  continuous  in  the  northern  hemisphere  except 
for  the  narrow  strait  or  sound  just  east  of  the  Ural  Mountains. 

Toward  the  close  of  the  Eocene  the  Pyrenees  Mountains  were 
upraised  by  folding,  while  initial  (though  moderate)  orogenic 
movements  took  place  in  the  regions  of  the  Apennines,  Alps,  and 
probably  Himalayas  as  well  as  some  other  mountain  districts. 


Fig.  187 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe  during 
Middle  Eocene  time.     (After  Kayser.) 

Oligocene.  —  The  Oligocene  is  best  known  in  Europe,  while  in 
many  other  parts  of  the  world  it  has  not  yet  been  separated  from 
the  Eocene  or  Miocene.  During  the  Oligocene  a  shallow  sea 
transgressed  over  northern  Germany.  In  many  places  there  were 
lagoons,  estuaries,  and  even  basins  in  which  terrestrial  deposits 
were  formed.  Some  beds  of  gypsum,  salt,  and  brown  coal  (lignite) 
were  formed.  Oligocene  strata  are  especially  well  developed 
throughout  southern  Europe.  In  Italy,  marine  deposits  of  this 
age  have  an  estimated  thickness  of  12,000  feet.  In  southern 
Europe  true  marine  conditions  prevailed,  though  continental 
deposition  also  occurred. 


THE  TERTIARY  PERIOD  307 

There  was  much  igneous  activity  during  this  epoch,  particularly 
in  Bohemia,  Ireland,  Scotland,  Iceland,  and  in  the  vicinity  of 
Vienna. 

More  or  less  severe  orogenic  movements  affected  certain  dis- 
tricts such  as  the  Balkan  and  Carpathian  Mountains  toward  the 
close  of  the  epoch. 

Oligocene  rocks  are  also  quite  certainly  present  in  the  Cau- 
casus Mountains,  southwestern  Asia,  and  northern  Africa,  but 
they  have  not  been  much  studied  in  other  countries. 


Fig.  188 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe 
during  Middle  Miocene  time.  Area  of  coarse  dots,  continental 
deposition;  areas  of  small  dots,  marine  waters.  (After  Kayser.) 

Miocene.  —  Viewed  in  a  broad  way,  the  Miocene  land  and 
water  areas  of  Europe  were  much  as  they  had  been  in  the  Eocene, 
all  but  the  northern  coast  of  Germany  again  becoming  dry  land. 
Marine  waters  occupied  parts  of  the  Atlantic  borders  of  France 
and  the  Iberian  peninsula,  while  southern  Europe  was  largely 
submerged  as  in  the  Eocene,  except  for  considerable  land  masses 
occupying  such  areas  as  the  interior  of  Spain  and  France,  portions 
of  the  sites  of  the  Alps,  Pyrenees,  Carpathians,  Apennines,  etc., 
which  had  been  more  or  less  affected  by  orogenic  movements  before 
the  Miocene  (see  map  Fig.  188).  A  remarkable  formation,  worthy 
of  special  mention,  is  an  extensive  conglomerate  several  thousand 
feet  thick  along  the  northern  side  of  the  present  Alps.  This  con- 


308 


HISTORICAL  GEOLOGY 


glomerate  has  considerably  controlled  the  topography,  for  instance 
in  the  vicinity  of  Lucerne. 

The  vast  Eocene  mediterranean  across  southwestern  Asia  was 
not  continued  into  the  Miocene.  Eocene  strata,  both  marine  and 
non-marine,  occur  in  northern  Africa  and  Syria,  but  not  in  the 
Persian  region.  Though  not  yet  well  studied,  Miocene  strata  are 
well  developed  in  southern  Asia,  Japan,  and  northeastern  Asia 
and  Australia.  In  South  America  the  Miocene  is  extensively 


Fig.  189 

Sketch  map  showing  the  relations  of  land  and  water  in  Europe 
during  Middle  Pliocene  time.  Small  dots,  marine  waters; 
coarse  dots,  areas  of  continental  deposition.  (After  Kayser.) 

shown  in  Argentina  and  probably  also  on  the  western  coast  of  the 
continent. 

Important  mountain  building  occurred  in  Europe  and  Asia 
in  the  middle  and  late  Miocene.  Though  initial  movements  had 
affected  the  sites  of  the  Alps,  Apennines,  and  probably  the  Him- 
alayas, these  mountains  were  greatly  elevated  by  tremendous 
orogenic  movements  in  the  Miocene.1  The  Caucasus  Mountains 

1  There  appears  to  be  some  doubt  as  to  whether  the  principal  orogenic 
movement  in  the  Himalayas  occurred  at  the  close  of  the  Eocene  or  in  the 
Miocene. 


THE  TERTIARY  PERIOD  309 

were  also  upraised  not  earlier  than  in  late  Miocene,  since  Miocene 
strata  are  there  found  about  7000  feet  above  sea-level. 

Considerable  igneous  activity  accompanied  the  late  Miocene 
erogenic  movements. 

Pliocene.  —  The  Pliocene  opened  with  comparatively  little  of 
Europe  under  marine  waters,  only  a  little  of  southern  England, 
Belgium,  the  northwestern  border  of  Germany,  a  little  of  southern 
France,  and  much  of  Italy  having  been  submerged  (see  map  Fig. 
189).  Only  in  Italy  are  thick  marine  deposits  known  where  the 
sediments  washed  from  the  newly  built  Apennines  accumulated 
to  a  thickness  of  from  1000  to  3000  feet.  Since  some  of  these 
deposits  now  lie  at  altitudes  of  2000  to  3000  feet,  it  is  evident  that 
the  Apennines  were  again  notably  upraised  after  the  deposition  of 
the  Pliocene  sediments.  Volcanoes  were  active  in  the  Mediter- 
ranean region,  especially  in  Italy  and  Sicily,  where  volcanoes  like 
Vesuvius  and  Etna  began  their  eruptions. 

In  southeastern  Europe  conditions  were  favorable  for  much 
deposition  of  continental  material  —  lake,  river,  and  terrestrial 
deposits. 

Marine  Pliocene  extends  up  the  Nile  Valley  for  many  miles. 
As  a  result  of  the  erosion  of  the  newly  upraised  Himalayas,  a 
deposit  of  sandstones,  conglomerates,  clays,  etc.,  several  thousand 
feet  thick,  accumulated  at  the  southern  base  of  those  mountains 
during  Pliocene  time. 

In  South  America  Pliocene  deposition  took  place  over  much  of 
southern  Argentina,  deposits  of  this  age  being  upturned  on  the 
eastern  flank  of  the  southern  Andes. 


CLIMATE 

During  the  Eocene  the  existence  of  a  subtropical  climate  well 
toward  the  northern  boundary  of  the  United  States,  and  in  Europe 
as  far  north  as  Germany  and  the  British  Isles,  is  abundantly  proved 
by  the  character  of  the  fossil  plants  and  animals. 

Over  the  Great  Plains  region  of  the  United  States  the  climate, 
now  semiarid,  was  distinctly  moister  during  the  earlier  Tertiary, 
because  the  great  deposits  of  lignite  prove  the  existence  of  prolific 
plant  life  in  swamps.  Fossil  Figs,  Palms,  and  Magnolias  in  the 
western  interior  indicate  much  warmer  and  moister  climate  than 
now.  This  was  in  harmony  with  what  we  know  of  the  physical 


310  HISTORICAL  GEOLOGY 

geography  of  the  west,  because  there  were  no  great  mountains  on 
the  Pacific  Coast  to  catch  most  of  the  moisture  from  the  westerly 
winds.  / 

Oligocene  climate  appears  to  have  been  somewhat  cooler 
(perhaps  warm-temperate)  in  western  North  America,  and  tropical 
in  southeastern  North  America.  In  Europe  the  warm  climate  of 
the  Eocene  seems  to  have  continued,  for  Palms  lived  in  northern 
Germany. 

During  Miocene  time  the  climate  of  the  Pacific  Coast  was 
almost  like  that  of  today.  On  the  Atlantic  Coast  a  comparatively 
cool  current,  apparently  from  the  north,  drove  out  the  warm  water 
forms  of  the  earlier  Tertiary.  In  the  western  interior  region  of  the 
United  States,  subtropical  plants  gave  way  to  temperate  climate 
plants.  In  Europe  the  warm  climate  of  the  earlier  Tertiary 
continued  into  the  earlier  Miocene  and  became  distinctly  cooler 
(temperate)  in  the  later  Miocene. 

The  Pliocene  was  in  general  cooler  than  the  Miocene,  in  fact, 
gradually  increasing  from  temperate  to  sub- Arctic  conditions  in 
the  waters  along  the  California  coast,  and  even  to  Arctic  conditions 
in  the  British  Isles  region.  Thus,  passing  upward  in  the  British 
Pliocene  series,  the  number  of  Arctic  fossil  forms  increases  from 
a  few  percent  to  50  or  60  percent.  An  exception  to  the  above 
general  conditions  appears  to  have  been  along  the  Atlantic  Coast 
of  the  United  States,  where  the  marine  water  was  rather  warmer 
than  it  had  been  during  the  Miocene.  As  judged  by  the  plants, 
the  lands  apparently  had  not  become  so  correspondingly  cold 
during  the  Pliocene. 

v 

ECONOMIC  PRODUCTS 

The  largest  production  of  petroleum  in  the  United  States  comes 
from  southern  California,  where  it  is  obtained  mostly  from  Tertiary 
shales  and  sandstones.  It  seems  certain  that  this  petroleum  origi- 
nated from  the  decomposition  of  countless  numbers  of  Diatoms 
in  certain  of  the  shales. 

Lignite  (or  brown  coal)  underlies  thousands  of  square  miles  of 
both  the  Gulf  States  and  the  western  interior  regions,  as  well  as 
smaller  areas  on  the  Pacific  Coast.  There  are  also  important 
lignite  deposits  in  Europe,  particularly  in  Germany. 

Many  important  gold  deposits  of  California  occur  in  Tertiary 


THE  TERTIARY  PERIOD 


311 


river  gravels,  which  are  often  capped  by  lava.  The  famous  gold 
deposits  of  Cripple  Creek,  Colorado,  and  Tonopah,  Nevada,  and 
the  copper  deposits  of  Butte,  Montana,  all  occur  as  veins  in,  or 
adjacent  to,  Tertiary  igneous  rocks. 

Valuable  phosphate  deposits  occur  in  the  Tertiary  limestones 
of  Florida. 

LIFE  OF  THE  TERTIARY 

Taken  as  a  whole,  the  life  of  the  Cenozoic  era  was  markedly 
different  from  that  of  the  Mesozoic.  Even  in  the  Tertiary  period 
the  most  important  groups  of  plants  and  animals  had  a  decidedly 
modern  aspect.  Most  of  the  plants  and  the  invertebrate  animals 
of  the  Tertiary  period  belonged  to  genera  which  still  exist,  while 
the  present-day  species  gradually  increased  from  a  small  percentage 
in  the  Eocene  to  a  large  percentage  in  the  Pliocene.  Among  the 
Vertebrates,  the  Fishes,  Amphibians,  Reptiles,1  and  Birds  differed 
but  little  from  those  of  today.  The  Mam- 
mals, however,  which  were  small,  primitive, 
and  relatively  rare  throughout  the  Mesozoic, 
showed  a  wonderful  development  both  in 
number  of  individuals  and  diversity  of  forms. 
The  Mammals  are,  therefore,  the  most  in- 
teresting and  characteristic  organisms  of 
Tertiary  time. 

PLANTS 


Fig.  190 

Diatoms  from  diato- 
maceous  earth  of  Ter- 
tiary age.  Greatly  en- 
larged. 


Vegetation  had  assumed  a  pretty  dis- 
tinctly modern  aspect  well  before  the  open- 
ing of  the  Cenozoic  era,  the  great  revolution 
from  ancient  to  modern  types  having  taken 
place  about  the  middle  of  the  Mesozoic  era. 
During  the  Tertiary,  however,  there  was 
notable  progress  toward  even  more  modern 
conditions,  so  that  many  genera  became  the  same  as  now  and  grad- 
ually more  and  more  present-day  species  were  introduced. 

Among  the  simplest  or  single-celled  plants,  the  Diatoms  deserve 
special  mention.  In  certain  times  and  places  they  swarmed  in  the 

1  Recently  a  few  Dinosaur  remains  have  been  found  in  the  earliest  Ter- 
tiary rocks,  but  otherwise  all  of  the  characteristic  Mesozoic  Reptiles  had 
become  extinct,  leaving  representatives  only  of  such  modern  groups  as  Liz- 
ards, Snakes,  Turtles,  Crocodiles,  and  a  few  other  water  forms. 


312  HISTORICAL  GEOLOGY 

Tertiary  waters.  "The  microscopic  plants  which  form  siliceous 
shells,  called  Diatoms,  make  extensive  deposits  in  some  places 
(Fig.  190).  One  stratum  near  Richmond,  Virginia,  is  30  feet  thick 
and  is  many  miles  in  extent;  another,  near  Monterey,  California, 
is  50  feet  thick,  and  the  material  is  as  white  and  fine  as  chalk, 
which  it  resembles  in  appearance;  another,  near  Bilin  in  Bohemia, 


Fig.  191 

A  well-preserved  fossil  Palm,  Thrimax  eocenica,  from  the  Eocene  of  Georgia. 
(After  Berry,  U.  S.  Geological  Survey,  Prof.  Paper  84.) 

is  14  feet  thick.  .  .  .  Ehrenberg  has  calculated  that  a  cubic  inch 

of  the  fine  earthy  rock  contains  about  forty-one  thousand  millions 

of  organisms.    Such  accumulations  of  Diatoms  are  made  both  in 

fresh  waters  and  salt,  and  in  those  of  the  ocean  at  all  depths."  1 

During  the  earlier  Tertiary,  as  we  have  learned,  the  climate  of 

Europe  and  the  northern  United  States  was  warm  temperate  to 

even  subtropical  and  there  flourished  such  trees  as  Palms  (Fig. 

1  J.  D.  Dana:  Text-book  of  Geology,  5th  ed.,  pp.  391-393. 


THE  TERTIARY  PERIOD  313 

191),  Laurels,  Oaks,  Willows,  Chestnuts,  etc.,  with  the  addition  of 
Magnolias,  Figs,  Poplars,  Ferns,  etc.,  in  the  western  interior  of  the 
United  States  and  southern  Canada.  As  far  north  as  Greenland 
and  Spitzbergen,  there  were  forests  with  Maples,  Camphor  trees, 
Figs,  Laurels,  Cypresses,  Poplars,  and  Sequoias.  The  Sequoias, 
which  are  of  special  interest,  began  in  the  late  Jurassic;  attained 
their  culmination  in  numbers  and  species  in  the  Tertiary;  and  are 
now  represented  by  only  two  species,  —  the  so-called  Big  Trees 
and  the  Redwoods,  —  which  are  wholly  confined  to  California. 
During  the  Tertiary  they  ranged  from  Greenland  on  the  north  to 
New  Zealand  on  the  south,  often  in  great  forests. 

In  the  later  Tertiary  the  distinctly  cooler  climate  in  the  higher 
latitudes  caused  a  disappearance  of  the  warm  climate  plants  such 
as  the  Palms  from  Europe,  and  the  Palms, 
Figs,  Magnolias,  etc.,  from  the  western  interior 
of  North  America. 

So  far  as  known,  the  Cereals  had  not  yet  ap- 
peared in  the  Tertiary,  but  the  Grasses  became 
abundant  and  must  have  had  an  important 
influence  in  the  development  of  the  principal 
groups  of  herbivorous  Mammals. 

An    Eocene    Fora- 
ANIMALS  ™n^r  Nummi^ 

lina    levigata. 

Since  the  Tertiary  invertebrates  were  in  (From  Le  Conte's 
nearly  every  way  so  similar  to  those  of  today,  "Geology,"  cour- 
we  shall  give  special  attention  to  only  a  few  tony  ^"  (?om_ 
features  of  interest.  pany.) 

Among  Protozoans,  the  Foraminifers  were 

exceedingly  abundant  and  often  remarkable  for  their  great  size. 
Of  these  the  Nummulites,  so  called  because  coin-shaped,  have  al- 
ready been  referred  to  as  making  up  great  limestone  deposits  in 
the  Old  World  Eocene.  They  attained  a  diameter  as  great  as 
half  an  inch  to  an  inch  (Fig.  192). 

Porifers,  Coelenterates,  Echinoderms,  and  Molluscoids  were 
almost  wholly  modern  in  character,  with  Crinoids  and  Brachiopods 
both  rare. 

Among  Mollusks  both  Pelecypods  (Figs.  193,  194)  and  Gastro- 
pods (Fig.  195)  were  exceedingly  common,  perhaps  more  so  than 
ever  before,  and  of  very  modern  aspect.  Oysters  appear  to  have 


314 


HISTORICAL  GEOLOGY 


reached  their  culmination  in  size  at  least,  some  having  grown  to  a 
length  of  ten  to  twenty  inches  and  a  width  of  six  or  eight  inches 
(Fig.  193).  Cephalopods,  as  we  have  learned,  diminished  remark- 
ably at  the  close  of  the  Cretaceous,  a  very  few  only  of  the  Ammo- 
nites and  Belemnites  having  straggled  into  the  Tertiary,  while  the 
Nautiloids  (e.g.  Nautilus)  were  more  diversified  and  widespread 


Fig.  193 

Large  Oyster  shells,  Ostrea  georgiana,  in  Eocene  strata  of  Georgia. 
L.  W.  Stephenson,  Geol.  Sur.  Ga.,  Bui.  26.) 


(After 


than  now.    The  Dibranchs  were  of  the  modern  Squid  and  Cuttle- 
fish types. 

Among  Arthropods  all  the  principal  groups  except  the  simplest 
(e.g.  Trilobites  and  Eurypterids)  were  represented,  the  Crabs 
among  the  Crustaceans  having  become  numerous  and  varied. 
Insects  are  known  in  far  greater  numbers  and  variety  than  from 
any  preceding  period.  All  the  important  groups  or  orders  were 
represented,  including  the  highest,  such  as  Moths,  Butterflies, 


THE  TERTIARY  PERIOD 


315 


Beetles,  Bees,  and  Ants.    The  prolific  vegetation  of  the  period  was 
of  course  very  favorable  for  Insect  development. 


a  b 

Fig.  194 

Tertiary  Pelecypods:  a,  Venericardia  marylandica  (Clark 
and  Martin);  b,  Pecten  choctanensis  (Aldrich).  (After 
Maryland  Geological  Survey.) 

In  a  single  Miocene  stratum  a  few  feet  thick  at  Oeningen,  near 
the  Swigs  border,  more  than_9QQLSfiecies  of  Insects  have  been  found. 
"In  some  places  the  stratum  is  black  with  the  remains  of  Insects. 


a  be 

Fig.  195 

Tertiary  Gastropods:  a,  Fulgur  carica;  b,  Strepsidura 
subcalarina;  c,  Turritella  potomacensis.  (All  from 
Maryland  Geological  Survey.) 


The  same  stratum  is  also  full  of  leaves  of  Dicotyls,  of  which  Heer 
has  described  500  species.    Mammalian  remains  and  also  Fishes 


316 


HISTORICAL  GEOLOGY 


are  found.  .  .  .  Doubtless,  at  Oeningen,  in  Miocene  times,  there 
was  an  extensive  lake  surrounded  by  dense  forests,  through  which 
ran  a  small  river  emptying  into  the  lake;  and  the  Insects  drowned 
in  its  waters,  and  the  leaves  strewn  by  the  winds  on  its  surface, 
were  cast  ashore  by  the  waves.  .  .  .  Over  500  of  the  Oeningen 
Insects  were  Beetles."  l 

Another  remarkable  occurrence  of  fossil  Insects  is  in  the  amber 
of  northern  Germany,  especially  on  the  shores  of  the  Baltic  Sea, 
where  fully  2000  species  have  been  obtained.  The  amber  is  a 


Fig.  196 

A  nearly  perfect  fossil  Teleost  Fish,  Diplomystus  densatus,  from  the  Eocene  of 
Wyoming.     (After  Veatch,  U.  S.  Geological  Survey,  Prof.  Paper  56.) 

fossil  resin  of  early  Oligocene  age  derived  from  certain  Conifers. 
The  Insects  were  caught  in  the  resin  while  it  was  still  soft  and 
sticky  and  they  were  thus  literally  embalmed  and  perfectly  pre- 
served to  the  present  day  in  the  often  quite  transparent  amber. 

At  Florissant,  Colorado,  certain  fresh  water  shales  of  Oligo- 
cene (?)  age  are  said  to  be  black  with  the  remains  of  Insects.  Over 
2000  species  are  represented  as  well  as  various  plants,  Fishes,  and 
even  a  Bird  with  well-preserved  feathers. 

Fishes.  —  These  were  in  general  much  like  those  of  the  later 
Mesozoic,  though  even  more  modern  in  aspect.  Teleosts  (Fig.  196) 
predominated,  but  Sharks  were  abundant  and  of  great  size  —  60 
to  80  feet  long  —  with  fossil  teeth  up  to  5  or  6  inches  long  occur- 

1  J.  Le  Conte:  Elements  of  Geology,  5th  ed.,  p.  534. 


THE  TERTIARY  PERIOD 


317 


ring  in  immense  numbers  in  some   places  as,  for  example,  the 
Atlantic  Coast  of  the  United  States  (Fig.  197). 

Amphibians.  —  After  the  culmination  of  their  development  in 
the  Triassic,  the  Amphibians  never  again  assumed  much  impor- 
tance. In  the  Tertiary  they  were  represented 
only  by  such  modern  types  as  Salamanders, 
Frogs,  and  Toads.  A  four-foot  skeleton  of  a 
Salamander  discovered  at  Oeningen,  Switz- 
erland, in  1728,  attracted  much  attention  for 
many  years.  It  was  called  "Homo  Diluvii 
Testis,"  because  it  was  considered  to  be  the 
skeleton  of  a  human  being  killed  during  the 
great  deluge  of  Noah. 

Reptiles.  —  These,  too,  were  quite  mod- 
ern, in  character,  with  Lizards,  Snakes  (all 
non-poisonous),  Crocodiles,  and  Turtles  all 
common  and  varied. 

Birds.  —  These  were  much  more  ad- 
vanced and  numerous  than  in  later  Mesozoic 
time,  and  many  of  the  modern  groups  had 
representatives.  A  few  of  the  more  primi- 
tive or  generalized  types,  however,  still  existed  in  the  early  Ter- 
tiary. Thus  a  toothed  Bird  has  been  found  in  the  Eocene  of 
England,  though  it  is  to  be  noted  that  the  teeth  were  not  set  in 
sockets  but  were  only  dentations  of  the  edge  of  the  bill  (Fig. 

198) .  Another  special  feature  was 
the  existence  of  very  large,  flight- 
less Ostrich-like  forms  which  at- 
tained heights  up  to  fully  10  feet. 
Mammals.  —  All  during  the 
Mesozoic  era  Mammals  existed, 
but  they  were  represented  only 
by  comparatively  few,  small, 
primitive  forms  which  always 
occupied  a  very  subordinate  posi- 
tion in  the  animal  world.  Very  early  in  the  Tertiary,  however, 
there  began  a  wonderful  development  of  Mammals.  Evolution  of 
many  of  the  higher  groups  went  on  rapidly,  so  that  by  the  close  of 
the  period  the  Mammals  had  become  differentiated  into  most  of  the 
principal  modern  types.  One  of  the  most  significant  features  in 


Fig.  197 

A  Shark's  tooth  from 
the  Eocene  of  the 
Gulf  Coastal  Plain. 
Length  of  tooth,  6 
inches.  (After  Gib- 
bes.) 


Fig.  198 

Head  of  an  Eocene  Bird,  Odontop- 
teryx  toliapicus,  showing  teeth. 
(After  Owen.) 


318 


HISTORICAL  GEOLOGY 


the  evolution  of  the  Mammals  during  the  Cenozoic  was  the  gradual 
increase  in  the  relative  sizes  of  the  brains.     The  accompanying 

sketches  graphically  illustrate 
this  fact  (Fig.  199). 

Mammals  comprise  the 
highest  of  all  animals  and  are 
all  characterized  by  suckling 
the  young.  For  convenience 
of  discussion,  they  may  be 
divided  into  three  groups  as 
follows :  (1)  Monotremes  or  egg- 
laying  forms,  such  as  the  mod- 
ern Spiny  Ant-eater;  (2)  Mar- 
supials (e.g.  Opossum  and 
Kangaroo)  or  those  giving 
birth  to  imperfectly  formed 
young,  which  are  then  carried 
by  the  mother  in  a  pouch 
(marsupium);  and  (3)  Placen- 
tals  (e.g.  Dog,  Horse,  and 
Man)  or  those  giving  birth  to 
well-formed  young  which,  in 
the  prenatal  condition,  are 
attached  to  the  mother  by  the 
placentum.  So  far  as  known, 
only  Monotremes  and  Mar- 
supials existed  during  the  Mes- 
ozoic,  but  during  the  Tertiary 
they  were  very  subordinate  to 
the  Placentals,  and  today  they 
are  comparatively  rare.  The 
Cenozoic  was,  (and  is)  there- 
fore, very  decidedly  the  "Age 
of  Placental  Mammals." 

Because  of  the  vast  wealth 


Fig.  199 

Sketches  to  illustrate  increase  in  size 
of  brains  of  Mammals  from  the 
Eocene  to  the  present.  A,  Eocene 
Uintatherium;  B,  Miocene  Bronto- 
therium;  C,  modern  Horse,  Equus. 
(After  Marsh,  from  Shimer's  "In- 
troduction to  the  Study  of  Fossils," 
courtesy  of  The  Macmillan  Com- 


pany.) 

of  material  concerning  Tertiary 

Mammals,  we  can  do  no  more,  in  our  brief  survey,  than  to  refer  to  a 

few  of  the  more  interesting  and  better  known  evolutionary  features. 

Generalized   Mammals    of   the    Early   Tertiary.  —  Although 

Mammals  were  the  dominant  animals  even  in  the  early  Tertiary, 


THE  TERTIARY  PERIOD  319 

nevertheless  they  were  not  then  differentiated  into  the  more  or 
less  clearly  defined  groups  of  today  such  as  the  Carnimzes.  or  flesh 
eaters  (e.g.  Dogs,  Bears,  Tigers,  etc.);  ^en&sodactyl§.  or  hoofed 
Mammals  with  an  odd  number  of  toes  (e.g.  Horses,  Rhinoceroses, 
etc.);  Arti.ofajdyls:  or  hoofed  Mammak-JHrith  an 


toes  (e.g.  Camels,  Deer,  Pigs,  etc.)  ;  Prob^ddians^  oTtFiihk-bearing: 

hoofed  Mammals   (e.g.   Elephants)  ^Ttodents,   or   gnawers    (e.g. 

Rats,  Squirrels,  etc.);    Insectivores  (e.g.  Moles,  Hedgehogs,  etc.); 

Cetaceans,  or  exclusively  swimmers  (e.g.  Whales,  Dolphins,  etc.); 

Pnggps,  or  the  very  highest  of   all  Mammals  (e.g.  Monkeys, 

Man,  etc.);   and  many  others. 

These  groups,  traced  back  to- 

ward the  early  Tertiary,  grad- 

ually become  less  and  less  dis- 

tinct until,  in  the  Eocene,  they 

cannot  be  at  all  distinguished 

as  separate  groups,  but  rather 

we  find  ancestral  or  generalized 

forms  which  show  combinations  Fig.  200 

of  features  of  the  later  groups.       A   nearly   perfect   skeleton   of   the 

One  of  the  most  character-         1f^e  CoP^taC°du8     primaems' 
istic  of  these  generalized  types 

of  the  early  Eocene  was  Phenacodus  (see  Fig.  200).  The  various 
species  of  this  genus  showed  about  the  same  range  in  size  as  modern 
Dogs.  Each  foot  had  five  toes  which  were  supplied  with  nails 
rather  between  true  claws  and  true  hoofs  in  structure.  The  simple 
(primitive)  teeth  indicate  that  the  animal  was  ononwerotis,  that 
is  both  plant  and  flesh  eating.  In  harmony  with  'other  "early  Ter- 
tiary Mammals,  the  brain  was  relatively  small  and  almost  devoid 
of  convolutions,  thus  pointing  to  a  low  grade  of  mental  devel- 
opment. I 

(e.g.  Horse).  •'As  an  example  of  the  history  of 


the  odd-toecOioofed,  Mammals,  we  shall  consider  the  well-known 
evolution  of  the  Horse  family.  At  least  forty  species  of  this  family, 
ranging  from  early  Eocene  to  the  present,  have  been  described, 
and  practically  every  connecting  link  in  the  evolution  of  the 
family  is  known.  Only  a  few  of  the  most  important  changes  can 
be  noted  in  our  brief  description,  which  is,  in  fact,  not  much  more 
than  an  explanation  of  the  excellent  chart  shown  in  Fig.  201.  The 
earliest  form,  called  Eohippus,  occurring  in  the  lower  Eocene,  was 


320 


HISTORICAL  GEOLOGY 


about  the  size  of  a  large  cat  (Fig.  202).  On  the  forefoot  it  had 
four  functional  toes  (one  larger  than  the  others)  and  a  splint  or 
imperfectly  developed  fifth  toe.  The  hind  foot  had  three  func- 
tional toes  and  a  splint.  Doubtless  this  early  member  of  the  Horse 
family  was  derived  from  an  original  five-toed  ancestor  1  whose 
general  structure  was  something  like  Phenacodus.  In  the  later 


Formations  in  Western  United  Stales  and  Characteristic  Type  of  Horse  in  Each  Fore  Foot 


Hypothetical  Ancestors  with  Five  Tots  on  Each  Foot 
and  Teelh  like  those  of  Monkeys  dc 


THE  EVOLUTION   OF  THE   HORSE. 


Fig.  201 

Chart  to  illustrate  the  evolution  of  the  Horse  family.    (After  W.  D.  Matthew, 
Amer.  Mus.  Nat.  Hist.  Journal.) 

Eocene  Protorohippus  had  four  distinct  toes  on  the  front  foot  and 
three  on  the  hindTbot,  but  with  no  sign  of  splints,  This  form  was 
but  little  larger  than  Eohippus.  During  the  Okgocene^Mesohippus 
had  three  functional  toes  (the  middle  one  being  dlstmctlylarger) , 
with  the  former  fourth  toe  reduced  to  a  splint  on  the  front  foot, 
while  the  three  functional  toes  continued  on  the  hind  foot.  It  was 
about  the  size  of  a  sheep.  In  the  MLoiiejie_.Prjo^oMp^s  had  three 
toes  on  both  fore  and  hind  feet,  but  in  each  case  only  one  was 

1  Very  recently  there  has  been  reported  the  discovery  of  a  still  more 
primitive  form,  even  more  closely  resembling  the  five-toed  ancestor. 


THE  TERTIARY  PERIOD  321 

large  and  functional,  with  the  other  two  small  toes  not- long  enough 
to  reach  the  ground.  This  form  was  about  the  size  of  a  pony. 
During  the  Pliocene  and  Quaternary, ^Equus,  or  the  modern  Horse, 
had  one  toe  only  "Oirtfont  ami  hind  feet  with  the  two  side  toes  of 
Protohippus  reduced  to  splints  (the  fetlock  of  the  present-day 
Horse).  Thus  we  see  that  the  middle  toe  of  the  original  five-toed 


Fig.  202 

Primitive  or  ancestral  Horses,  Eohippus,  of  the  Eocene.  Restored  by  C.  R. 
Knight  under  the  direction  of  H.  F.  Osborn.  (Permission  of  American 
Museum  of  Natural  History.) 

ancestor  has  developed,  to  the  exclusion  of  the  others,  and  it  is 
thought  that  this  has  tended  toward  greater  fleetness  of  foot. 
While  these  evolutionary  changes  took  place,  there  was  also  gradu- 
ally developed  longer  and  more  complex  teeth;  the  two  entirely 
separate  bones  (radiiis_jjid_ulna)  of  th^Joj^ij]ab_gradually  became 
consolidated  into  a  single  strong  bone;  and  the  brain  steadily 
increased  in  relative  size. 

(e.g.   Camel).     These  even-toed,   hoofed   Mam- 


322 


HISTORICAL  GEOLOGY 


mals  (Fig.  203) ,  like  the  odd-toed  ones,  were  descended  from  a 
five-toed  Eocene  ancestor.     In  their  development  the  first  toe 


Fig.  203 

Evolution  of  foot  of  even-toed  (Artiodactyl)  Mammals  illustrated 
by  existing  forms.  A,  Pig;  B,  Roebuck;  C,  Camel.  (From 
Norton's  "Elements  of  Geology,"  by  permission  of  Ginn  and 
Company,  Publishers.) 

disappeared,  while  the  middle  pair  of  the  remaining  four  became 
larger  and  the  two  side  toes  became  smaller  and  smaller,  having 

disappeared  altogether  in  such 
a  type  as  the  modern  Camel. 
This  sort  of  evolution  in  the 
Camel  family  has  been  traced 
in  almost  as  much  detail  as  in 
the  Horse  family.  Beside  the 
Fig  204  Camel,  other  two-toed  existing 

a,  Mastodon  tooth;  6,  Mammoth  tooth.     forms    are    Deer>    Cattle>    and 
Both  viewed  from  the  side.  Sheep.     The    two-toed   Artio- 

dactyls  now  predominate,  while 

the  four-toed  forms   (at  present  represented  e.g.  by  Hogs  and 
Hippopotami)  culminated  in  the  Tertiary. 

Elephant).     This  group  of  hoofed  Mam- 


THE  TERTIARY  PERIOD 


323 


mals,  characterized  by  the  proboscis  (trunk),  has  been  traced 
through  many  intermediate  forms  back  to  primitive  Eocene 
ancestry.  Proboscidians  culminated  in  the  Pliocene,  when  they 
were  the  largest  (up  to  13  or  14  feet  high),  the  most  numerous,  and 
widespread  over  much  of  the  earth  except  Australia.  Mastodons, 
now  wholly  extinct,  are  characterized  by  having  knob-like  promi- 


Fig.  205 

A  Mammoth  Elephant,  Elephas  primigenius,  restored  by  C.  R.  Knight.    (Per- 
mission of  American  Museum  of  Natural  History.) 

nences  on  the  chewing  surfaces  of  their  large  teeth  (Fig.  204a), 
while  the  true  Elephants  (including  the  extinct  Mammoths)  have 
large  nearly  flat  grinding  surfaces  orr  their  teeth  (Fig.  204b).  True 
ElepMnts  ateo  nearly  always  show  greater  curvature  of  the  tusks. 
The  Mammoth  had  long  brown  hair  (Fig.  205) . 

The  accompanying  sketches  (Fig.  206),  together  with  the 
following  excellent  summary  by  Lull,  will  give  a  good  idea  of  the 
evolution  of  the  Proboscidians.  "  Increase  in  size  and  in  the  de- 


324 


HISTORICAL  GEOLOGY 


Mastodon  '/Q 


WOOLEM/OCENE  \ 

Miration  into  \ 

LOMR  MIOCEMY 


iOmOL/COCENE 


PataeonasTodon'fy  UPPER  EOCENE 


MIOOUEOCENE 


Pa/aeomasfodon 
(lengthtnino  chin 


Moeritherium 

(Shortc/im) 


.  Moeritier/um  ft 


L  OWfft  EOCfME  (offfCSfor  untnowri). 


Fig.  20o 

Chart  to  illustrate  the  evolution  of  the  Elephants.  (From  Scott, 
after  Lull,  modified  by  Sinclair,  by  courtesy  of  The  Macmillan 
Company.) 


THE  TERTIARY  PERIOD  325 

velopment  of  pillar-like  limbs  to  support  the  enormous  weight. 
Increase  in  size  and  complexity  of  the  teeth  and  their  consequerff 
diminution  in  numbers  and  the  development  of  the  peculiar  method 
of  tooth  succession.  The  loss  of  the  canines  and  of  all  of  the  incisor 
teeth  except  the  second  pair  in  the  upper  and  lower  jaws  and  the 
development  of  these  as  tusks.  The  gradual  elongation  of  the 
symphysis  or  union  of  the  lower  jaws  to  strengthen  and  support 
the  lower  tusks  while  digging,  culminating  in  Tetrabeledon  (or 
Gomphotherium)  Angustidens.  The  apparently  sudden  shortening 
of  this  symphysis  following  the  loss  of  the  lower  tusks  and  the  com- 
pensating increase  in  size  and  the  change  in  curvature  of  those  of 
the  upper  jaw. 

"The  increase  in  bulk  and  height,  together  with  the  shortening 
of  the  neck  necessitated  by  the  increasing  weight  of  the  head  with 
its  great  battery  of  tusks,  necessitated  the  development  of  a  pre- 
hensile upper  lip  which  gradually  evolved  into  a  proboscis  for  food 
gathering.  The  elongation  of  the  lower  jaw  implies  a  similar 
elongation  of  this  proboscis  in  order  that  the  latter  may  reach 
beyond  the  tusks.  The  trunk  did  not,  however,  reach  maximum 
utility  until  the  shortening  jaw,  removing  the  support  from  be- 
neath, left  it  pendant,  as  in  the  living  Elephant."  1 

Carnivores  (Tigers,  Dogs,  etc.).  These  modern  flesh-eaters 
can  be  traced  back  to  a  generalized  order  or  group  (so-called 
Creodonts,  Fig.  207)  which  had  certain  characters  suggesting  the 
Insect-eaters,  hoofed  Mammals,  and  Marsupials,  as  well  as  the 
Carnivores.  These  Creodonts  or  ancestral  flesh-eaters  had  small, 
simple  brains  and  many  small  teeth.  In  the  course  of  evolution 
the  existing  carnivorous  families  have  been  derived  from  them. 

I&denLs_  (Rats,  Porcupines,  Squirrels,  etc.).  The  Rodents. 
(gnawers)  can  be  traced  back  to  the  early  Eocene,  when  the  incisor 
teeth  were  just  developing  a  structure  suitable  for  gnawing.  By 
the  middle  of  the  Eocene  the  Rodents  were  common  and  their 
incisors  were  highly  specialized  for  gnawing.  Primitive  Squirrel- 
like  forms  are  known  from  the  late  Eocene. 

ImectivQres  (e.g.  Moles,  Hedgehogs,  etc.).  These  have  also 
been  traced  back  to  the  Eocene,  and,  like  the  Rodents,  they  still 
show  many  of  their  ancestral  or  primitive  features.  They  have 
changed  much  less  than  most  of  the  other  classes  of  Mammals. 

Cetaceans    (e.g.   Whales,    Porpoises,  etc.).    In   our   study   of 
1  R.  S.  Lull:  Amer.  Jour.  Sci.,  Vol.  25,  1908,  pp.  11-13. 


326 


HISTORICAL  GEOLOGY 


Fig.  207 

Skeleton  of  an  Eocene  Creodont,  Patriofelis.     (After  Osborn,  from  Cham- 
berlin  and  Salisbury's  "Geology,"  courtesy  of  Henry  Holt  and  Company.) 

Mesozoic  Reptiles  we  found  that  certain  forms  took  to  the  sea 
and  became  truly  marine  Fish-like  creatures,  such  as  the  Ichthyo- 

saur  and  the  Mosasaur.  So 
in  the  Tertiary  (even  in  the 
Eocene)  certain  Mammals  be- 
came so  adapted  to  the  water 
environment  as  to  become 
Fish-like  forms,  such  as 
Whales,  Porpoises,  etc.,  which 
are  often  popularly  regarded 
as  true  Fishes.  Apparently 
we  have  here  an  example  of 
-  208  retrogression  in  evolution,  be- 

One  of  the  earliest   Monkeys,   Meso-      cauge  true  }an(j  animals  took 

rKr— mbh;  ST;  *> «» watered  t^  iegs 

Length    of    specimen,     about    20      degenerated    into    swimming 
inches.  paddles.     Certain  Whale-like 

forms    (Zeuglodons)     of    the 

Eocene  reached  lengths  up  to  60  or  80  feet  and  must  have  been 
extremely  abundant,  their  vertebrae  often  being  found  in  great 
numbers  in  Alabama  and  other  places. 


THE  TERTIARY  PERIOD  327 

(e.g.  Lemurs)  and  Pwmaies-  (e.g.  Monkeys,  Apes, 
and  Man).  These  two  groups  include  the  highest  of  all  animals. 
During  the  Eocene  "  Numerous  Lemuroids  and  primitive  types  of 
Monkeys  swarmed  in  the  trees"  (W.  B.  Scott).  True  Monkeys 
and  Apes,  however,  did  not  appear  till  in  the  Miocene  (Fig.  208). 
A  partial  skeleton,  known  as  Pithecarithi^us^reQ^s,  discovered  in^ 
Java  (1891)  in  deposits  possibly  of  Pliocene  age,  has  been  the  cause 
ofmuch  discussion.  This  creature  appears  to  have  had  characters 
intermediate  between  the  lowest  types  of  Men  and  the  highest 
types  of  Apes,  but  the  bones  have  elicited  much  difference  of  opin- 
ion. By  some  they  are  regarded  as  those  of  an  ancestral  type  of 
Man;  by  others  as  those  of  an  abnormal  human  being;  and  by  still 
others  as  those  of  a  large  Ape. 

So  far  as  present  knowledge  goes,  we  have  no  positive  evidence 
that  Man  appeared  on  the  earth  even  late  in  the  Tertiary,  though 
future  discoveries  may  trace  his  ancestry  that  far  back.  The 
antiquity  of  Man  will  be  further  discussed  toward  the  close  of  the 
next  chapter. 


CHAPTER  XIX 
THE   QUATERNARY  PERIOD 

BY  the  very  nature  of  the  case,  our  usual  method  of  discussion 
cannot  be  applied  to  the  Quaternary  period  without  considerable 
modification,  the  characteristic  feature  having  been  vast  sheets 
of  ice  covering  much  of  the  northern  hemisphere.  Otherwise  the 
earth  had  reached  essentially  its  present  geological  condition. 

ORIGIN  OF  NAME,  SUBDIVISIONS,  ETC. 

As  pointed  out  toward  the  beginning  of  the  last  chapter,  the 
terms  " Tertiary"  and  "Quaternary"  are  both  remnants  of  an  old 
geological  nomenclature,  and  both  have  entirely  lost  their  original 
significance.  The  Quaternary  is  the  last  great  period  of  earth 
history,  the  study  of  which  leads  us  right  up  to  present-day  geo- 
graphic and  geologic  conditions.  During  this  period  nearly  all  of 
the  existing  species  of  invertebrates  and  lower  Vertebrates,  as  well 
as  most  of  the  existing  species  of  Mammals,  had  appeared.  Except 
in  the  glaciated  regions,  the  line  of  separation  between  the  Tertiary 
and  the  Quaternary  is  not  at  all  clearly  defined. 

Following  the  usual  method,  we  shall  divide  the  Quaternary 
period  into  (1)  the  Pleistocene  or  Glacial  epoch,  which  represents 
the  time  of  ice  occupation  of  northern  North  America  and  northern 
Europe,  and  (2)  the  Recent  or  post-Glacial  epoch  or  time  since  the 
removal  of  the  ice  from  those  continents.  We  are  living  in  the 
Recent  epoch. 

THE  FACT  OF  THE  ICE  AGE 

The  Quaternary  period  was  ushered  in  by  the  spreading  of  vast 
ice  sheets  over  much  of  northern  North  America  and  northern 
Europe.  This  event  must  take  rank  as  one  of  the  most  interesting 
and  remarkable  occurrences  in  geological  time.  On  first  thought, 
the  existence  of  such  vast  ice  sheets  seems  unbelievable,  but  the 
Ice  age  occurred  so  short  a  time  ago  that  the  records  of  the  event 
are  perfectly  clear  and  conclusive.  The  fact  of  this  great  Ice  age 
was  discovered  by  Louis  Agassiz  in  1837,  and  fully  announced 

328 


THE  QUATERNARY  PERIOD  329 

before  the  British  Scientific  Association  in  1840.  For  some  years 
the  idea  was  opposed,  especially  by  advocates  of  the  so-called  ice- 
berg theory.  Now,  however,  no  important  event  of  earth  history 
is  more  firmly  established  and  no  student  of  the  subject  ever 
questions  the  fact  of  the  Quaternary  Ice  age. 

Some  of  the  proofs  for  the  former  presence  of  the  great  ice 
sheets  are  as  follows:  (1)  Polished  and  striated  rock  surfaces 
which  are  precisely  like  those  produced  by  existing  glaciers,  and 
which  could  not  possibly  have  been  produced  by  any  other 
agency;  (2)  glacial  boulders  or  " erratics,"  which  are  often  some- 
what rounded  and  scratched,  and  which  have  often  been  trans- 
ported many  miles  from  their  parent  rock  ledges;  (3)  true 
glacial  moraines,  especially  terminal  moraines,  like  that  which 
extends  the  full  length  of  Long  Island  and  marks  the  southern- 
most limit  of  the  ice  sheet  there;  (4)  the  generally  widespread 
distribution,  over  most  of  the  glaciated  area,  of  heterogeneous 
glacial  debris  (so-called  " drift")  both  unstratified  and  stratified, 
which  is  clearly  transported  material  and  typically  rests  upon 
the  bed-rock  by  sharp  contact.  In  regions  which  have  not  been 
glaciated,  it  is  quite  the  rule  to  find  that  the  underlying  fresh  rock 
grades  upward  through  rotten  rock  into  soil. 

ICE  EXTENT  AND  CENTERS  OF  ACCUMULATION 

The  best  known  existing  ice  sheets  are  those  of  Greenland  and 
Antarctica,  particularly  the  former,  which  covers  about  500,000 
square  miles.  This  glacier  is  so  large  and  deep  that  only  an 
occasional  high  rocky  mountain  projects  above  its  surface,  and  the 
ice  is  known  to  be  slowly  moving  outward  in  all  directions  from  the 
interior  to  the  margins  of  Greenland.  Along  the  margins,  where 
melting  is  more  rapid,  some  land  is  exposed,  but  often  the  ice  flows 
out  into  the  ocean,  where  it  breaks  off  to  form  large  icebergs. 

The  accompanying  map  Fig.  209  shows  the  area  of  nearly 
4,000,000  square  miles  of  North  America  covered  by  ice  at  the  time 
of  maximum  glaciation,  and  also  the  three  great  centres  of  accumu- 
lation and  dispersal  of  the  ice.  The  directions  of  flow  of  the  ice 
from  these  centres  have  been  determined  by  the  study  of  the  direc- 
tions of  a  very  large  number  of  glacial  striae,  as  well  as  the  direction 
of  transportation  of  the  glacial  debris.  Greenland  was  also  buried 
under  ice  during  the  Quaternary  period. 


330 


HISTORICAL  GEOLOGY 


Two  striking  features  regarding  the  distribution  of  the  ice  were 
(1)  the  failure  of  the  ice  to  cover  any  of  Alaska  except  its  high 
southern  mountain  region,  though  that  country  is  much  farther 
north  than  most  of  the  glaciated  area;  and  (2)  the  failure  of  any- 


Fig.  209 

Map  showing  the  areas  occupied  by  ice  in  North  America  at  the 
time  of  maximum  glaciation.  The  three  great  centres  of  dispersal 
are  indicated.  (After  Salisbury,  from  Norton's  "Elements  of  Geol- 
ogy/' by  permission  of  Ginn  and  Company,  Publishers.) 

thing  like  continuous  ice  sheets  over  the  high  plateaus  of  the  west- 
ern United  States,  while  the  great  ice  sheet  spread  over  much  of  the 
low  plains  area  of  the  upper  Mississippi  Basin. 

From  its  centre  of  accumulation,  the  Labradorean  ice  sheet 
extended  fully  1600  miles  south  west  ward  or  to  about  the  mouth 
of  the  Ohio  River.  The  Kewatin  sheet  extended  from  its  centre 


THE  QUATERNARY  PERIOD  331 

southward  nearly  as  far,  or  into  northern  Missouri.  These  two 
great  ice  sheets  practically  merged.  "One  of  the  most  marvelous 
features  of  the  ice  dispersion  was  the  great  extension  of  the  Kewatin 
sheet  from  a  low  flat  centre  westward  and  southwestward  over  what 
is  now  a  semiarid  plain,  rising  in  the  direction  in  which  the  ice 
moved,  while  the  mountain  glaciers  on  the  west,  where  now  known, 
pushed  eastward  but  little  beyond  the  foothills"  (Chamberlin 
and  Salisbury). 

The  Cordilleran  ice  sheet  appears  to  have  been  mostly  made 
up  of  both  plateau  and  typical  mountain  (Alpine)  glaciers.  To- 
ward the  south  it  extended  only  a  little  way  over  the  high  moun- 
tains of  the  northwestern  United  States. 

Newfoundland,  and  possibly  also  Nova  Scotia,  had  local  centres 
of  glaciation. 

South  of  the  ice  sheets  above  described,  the  higher  mountains 
of  the  United  States,  even  as  far  south  as  southern  California, 
Arizona,  and  New  Mexico,  bore  numerous  glaciers  greatly  varying 
in  size.  These  were  always  of  the  typical  valley  or  Alpine  types 
instead  of  ice  sheets.  Some  of  these  mountains,  such  as  Shasta, 
Hood,  Rainier,  and  those  of  the  Glacier  National  Park  in  Montana, 
still  have  glaciers,  the  greatest  being  those  of  Mount  Rainier,  where 
they  attain  lengths  of  from  4  to  6  miles. 

DIRECTION  OF  MOVEMENT  AND  DEPTH  OF  ICE 

The  fact  that  glacial  ice  flows  as  though  it  were  a  viscous  sub- 
stance is  well  known  from  studies  of  present-day  glaciers  in  the 
Alps,  Alaska,  and  Greenland.  A  common  assumption,  either  that 
the  land  at  the  centre  of  accumulation  must  have  been  thousands 
of  feet  higher,  or  that  the  ice  must  have  been  immensely  thick,  in 
order  to  prevent  flowage  so  far  out  from  the  centre,  is  not  necessary. 
For  instance,  if  one  proceeds  to  pour  viscous  tar  slowly  in  one  place 
upon  a  perfectly  smooth  (level)  surface,  the  substance  will  gradu- 
ally flow  out  in  all  directions,  and  at  no  time  will  the  tar  at  the 
centre  of  accumulation  be  very  much  thicker  than  at  other  places. 
The  movement  of  the  ice  from  each  of  the  great  centres  was  much 
like  this,  only  in  the  case  of  the  glacier  the  piling  up  of  snow  and 
ice  was  by  no  means  confined  to  the  centres  of  accumulation. 

Some  of  the  finest  examples  of  the  influence  of  topography 
upon  the  direction  of  movement  of  the  ice  are  afforded  by  New 


332  HISTORICAL  GEOLOGY 

York  state  on  account  of  its  peculiar  relief  features.  When  the 
Labradorean  ice  sheet  spread  southward  as  far  as  northern  New 
York,  the  Adirondack  Mountains  stood  out  as  a  considerable 
obstacle  in  the  path  of  the  moving  ice,  and  the  tendency  was  for 
the  current  to  divide  into  two  portions,  one  of  which  passed  south- 
westward  up  the  low,  broad  St.  Lawrence  Valley,  and  the  other 
due  southward  through  the  deep,  narrow  Champlain  Valley.  As 
the  ice  kept  crowding  from  the  rear,  part  of  the  St.  Lawrence  ice 
lobe  pushed  into  the  Ontario  basin,  while  another  portion  worked 
its  way  up  the  broad,  low  Black  River  Valley  and  finally  into  the 
Mohawk  Valley.  At  the  same  time  the  Champlain  ice  lobe  found 
its  way  into  the  upper  Hudson  Valley,  and  sent  a  branch  lobe 
westward  up  the  broad,  low  Mohawk  Valley.  The  two  Mohawk 
lobes,  the  one  from  the  west  and  the  other  from  the  east,  met  in 
the  midst  of  the  Mohawk  Valley.  As  the  ice  sheet  continued  to 
push  southward,  all  the  lowlands  of  northern  New  York  were 
filled;  a  tongue  or  lobe  was  sent  down  the  Hudson  Valley;  and 
finally  the  whole  state,  except  slight  portions  of  the  southern 
border,  was  buried  under  the  ice.  The  general  direction  of  flow  at 
this  time  of  maximum  glaciation  was  southward  to  south  west  ward, 
with  perhaps  some  undercurrents  determined  by  the  larger  topo- 
graphic features.  Thus  we  learn  that  the  major  relief  features  of 
the  state  very  largely  determined  the  direction  of  ice  currents,  ex- 
cept at  the  time  of  maximum  glaciation,  when  only  the  under- 
currents were  controlled.  These  ideas  are  abundantly  borne  out  by 
the  distribution  of  glacial  striae  and  boulders  over  the  state. 

Evidences  of  glaciation,  such  as  striae,  boulders,  lakes,  etc., 
occur  high  up  in  the  Adirondacks,  the  Catskills,  the  Green  and  the 
White  Mountains,  and  the  Berkshire  Hills,  so  that  the  greatest 
depth  of  ice  over  New  York  and  New  England  could  not  have  been 
less  than  some  thousands  of  feet.  In  fact  we  have  every  reason  to 
believe  that  all  of  the  mountains  named,  except  possibly  the 
Catskills,  were  completely  buried.  The  reader  may  wonder  how 
an  ice  sheet  a  mile  thick  in  northern  New  York  could  have  thinned 
out  to  disappearance  at  or  near  the  southern  border  of  the  state, 
but  observations  on  existing  glaciers  show  that  it  is  quite  the  habit 
of  extensive  ice  bodies  to  thin  out  very  rapidly  near  the  margins, 
thus  producing  steep  slopes  along  the  ice  fronts. 

There  is  little  reason  to  doubt  that  the  vast  ice  sheet  over  the 
upper  Mississippi  Valley  was  also  thousands  of  feet  thick.  The 


THE  QUATERNARY  PERIOD  333 

positions  of  the  moraines  there  clearly  prove  that  the  ice  front 
was  more  or  less  distinctly  lobate. 


SUCCESSIVE  ICE  INVASIONS 

The  front  of  the  great  ice  sheet,  like  that  of  ordinary  valley 
glaciers,  must  have  shown  many  advances  and  retreats.  In  the 
northern  Mississippi  Valley,  however,  we  have  positive  proof  of 
several  (perhaps  five  of  six)  important  advances  and  retreats  of 
the  ice  which  gave  rise  to  true  interglacial  stages.  The  strongest 
evidence  is  the  presence  of  successive  layers  of  glacial  debris,  a  given 


Fig.  210 

Diagram  to  show  how  successive  glacial  drift  sheets  are 
distinguished.  N  to  m,  younger  drift;  m  to  S,  surface  of 
older  drift.  Surface  of  younger  drift  almost  unaffected  by 
erosion  and  weathering,  while  the  older  drift  is  notably 
dissected  and  its  surface  considerably  weathered.  A 
distinct  terminal  moraine  at  m  marks  end  of  younger 
drift  sheet.  Heavy  black  bands  represent  deposits  of 
organic  matter. 

layer  often  having  been  oxidized,  eroded,  and  covered  with  vegeta- 
tion before  the  next  (overlying)  layer  was  deposited  (see  Fig.  210). 
In  drilling  wells  through  the  glacial  deposits  of  Iowa,  for  example, 
two  distinct  layers  of  vegetation  are  often  encountered  at  depths 
of  from  100  to  200  feet.  Near  Toronto,  Canada,  plants  which 
actually  belong  much  farther  south  in  a  warm  climate  have  been 
found  between  two  layers  of  glacial  debris.  Thus  we  know  that 
some,  at  least,  of  the  ice  retreats  produced  interglacial  stages  with 
warmer  climate  and  were  sufficient  greatly  to  reduce  the  size  of  the 
continental  ice  sheet  or  possibly  to  cause  its  entire  disappearance. 
By  applying  the  principles  just  laid  down,  at  least  five  advances 
and  retreats  of  the  ice,  with  distinct  interglacial  intervals  have 
been  recognized  in  North  America  as  follows:  (1)  Pre-Kansan  or 
Jerseyan;  (2)  Kansan;  (3)Illinoian;  (4)  lowan;  and  (5)  Wisconsin.1 

1  The  Wisconsin   invasion   is  sometimes   divided   into  two  —  an  early 
and  a  late  Wisconsin. 


334  HISTORICAL  GEOLOGY 

In  New  York  and  New  England  no  very  positive  evidence  has 
as  yet  been  found  to  prove  truly  multiple  glaciation,  though  some 
phenomena  as,  for  example,  certain  buried  gorges,  are  difficult  to 
account  for  except  on  the  basis  of  more  than  one  advance  and 
retreat  of  the  ice.  At  any  rate  there  appears  to  be  no  good  reason 
whatever  to  believe  that  there  were  more  than  two  advances  and 
retreats  of  the  ice  over  this  region. 

For  our  purpose  in  considering  only  the  general  effects  of 
glaciation,  we  may  practically  disregard  the  problem  of  multiple 
glaciation,  because  the  final  effects  would  have  been  essentially 
the  same  as  a  result  of  a  single  great  glacial  advance  and  retreat. 

THE  DRIFTLESS  AREAS 

In  southwestern  Wisconsin,  and  extending  a  little  into  Iowa 
and  Illinois,  there  is  a  non-glaciated  area  of  about  10,000  square 
miles  which  lies  several  hundred  miles  north  of  the  southern  limit 
of  the  ice  sheets  (see  Fig.  209).  This  is  called  a  "driftless  area," 
because  of  the  utter  absence  of  glacial  debris  or  any  other  evi- 
dence of  glaciation  within  its  boundary.  In  spite  of  several  ice 
invasions  on  all  sides,  this  srnall  area  was  never  ice  covered. 
Residual  soils  and  rotten  rock  are  widespread;  there  are  no  lakes; 
and  the  streams  are  mostly  graded  and  without  waterfalls  or 
rapids.  This  small  region,  therefore,  gives  an  excellent  idea  of 
the  kind  of  topography  which  the  whole  upper  Mississippi  Valley 
would  have  shown  had  it  not  been  for  the  glaciation.  At  no 
time. did  the  Labradorean  ice  sheet  spread  far  enough  eastward, 
or  the  Kewatin  sheet  far  enough  westward,  to  cover  this  driftless 
area.  The  highland  district  just  south  of  Lake  Superior  doubt- 
less served  to  deflect  and  weaken  the  flow  of  the  Labradorean  ice 
which  otherwise  might  have  spread  far  enough  to  have  covered 
the  driftless  area. 

A  much  smaller  driftless  area  has  more  recently  been  discovered 
along  the  Mississippi  River  in  Missouri.  It  is  not  difficult  to 
understand  why  such  an  area  so  close  to  the  southern  limit  of 
glaciation  escaped  all  advances  of  the  ice  sheets. 

ICE  EROSION 

Ice,  like  flowing  water,  has  very  little  erosive  effect  unless  it  is 
properly  supplied  with  tools.  When  flowing  ice  is  shod  with  hard 


THE  QUATERNARY  PERIOD  335 

rock  fragments  the  power  to  erode  is  often  pronounced,  because 
the  work  of  abrasion  is  mostly  accomplished  by  the  rock  fragments 
embedded  in  the  ice  rather  than  by  the  soft  ice  itself.  For  instance, 
when  the  great  ice  lobe  moved  up  the  St.  Lawrence  Valley  it  was 
shod  with  many  pieces  of  hard  pre-Cambrian  rocks,  and  the  effects 
of  erosion  are  remarkably  well  shown  in  the  Thousand  Islands 
region,  where  successions  of  great  grooves  cut  in  the  solid  rock 
may  often  be  seen.  A  little  search  will  reveal  polished  and 
scratched  or  grooved  rock  surfaces  in  almost  any  part  of  the 


Fig.  211 

Smoothed  and  striated  (glaciated)  limestone. 
(W.  J,  Miller,  photo.) 

glaciated  region  of  the  continent  (Fig.  211).  Hard  rock  ledges 
most  frequently  exhibit  glacial  marks,  and  the  freshness  and 
hardness  of  such  surface  rock  proves  that  the  ice  eroded  all 
of  the  deep  residual  soil  as  well  as  the  zone  of  rotten  rock,  and  an 
unknown  amount  of  live  or  fresh  rock. 

In  former  years  a  very  great  erosive  power  was  ascribed  to 
flowing  ice,  but  today  some  glacialists  consider  ice  erosion  to  be 
almost  negligible,  while  many  others  maintain  that,  under  favor- 
able conditions,  flowing  ice  may  produce  very  notable  erosive 
effects.  During  the  long  pre-Glacial  time,  rock  decomposition 
must  have  progressed  so  far  that  rotten  rock,  including  soils,  had 


336  HISTORICAL  GEOLOGY 

accumulated  to  considerable  depths,  as  today  in  the  southern 
states.  Such  soils  are  called  "residual,"  because  they  are  derived 
by  the  decomposition  of  the  very  rocks  on  which  they  rest.  But 
now  one  rarely  sees  rotten  rock  or  soil  in  its  original  position  well 
within  the  glaciated  area,  because  such  materials  were  nearly  all 
scoured  off  by  the  passage  of  the  great  ice  sheet,  mixed  with  other 
soils  and  ground  up  rock  fragments,  and  deposited  elsewhere. 
Such  are  called  transported  soils.  Along  the  southern  side  of  the 


k?;«&tj  Glacial  Sake  de/ta  deposit  \     I     I  Trenton 

V.V.;:]  Osweyo    sandstone  ('::f-'-'-)  ^bme//a-l.oiou/7/e    /imestor/e 

•  •  •  •  •  |  Lorrame  sha/e  <f  sandstone  |-^=~— |  Pa/eo?otc  strata  (corjcea/ed) 

rz_  ^J  Utica    sha/e  |/^_X1  Precom^r/c    roc As 


Fig.  212 

Structure  section  across  the  Black  River  Valley  of  northern  New  York  to 
illustrate  the  effect  of  ice  erosion  and  glacial  lake  deposition.  Note  the 
steep  front  of  the  shale  terrace  which  has  been  produced  by  ice  erosion, 
and  the  conspicuous  delta  deposit  of  the  extinct  glacial  lake  on  the  east 
side.  The  surface  of  the  delta  deposit  represents  the  former  lake  level. 
(After  W.  J.  Miller,  N.  Y.  State  Mus.,  Bui.  135.) 

glaciated  area,  where  the  erosive  power  of  the  ice  was  least,  rotten 
rock  is  more  common.  Ice,  shod  with  hard  rock  fragments  and 
flowing  through  a  deep,  comparatively  narrow  valley  of  soft  rock, 
is  especially  powerful  as  an  erosive  agent,  because  the  tools  are 
supplied,  the  work  to  be  done  is  easy,  and  the  increased  depth  of 
the  ice  where  crowded  into  a  deep,  narrow  valley  causes  greater 
pressure  on  the  bottom  and  sides  of  the  channel.  Many  of  the 
valleys  of  northern  New  York  were  thus  favorably  situated  for 
ice  erosion,  as,  for  example,  the  Champlain,  St.  Lawrence,  Black 
River,  Finger  Lakes  valleys.  The  writer  has  made  a  special  study 
of  ice  erosion  in  the  Black  River  Valley  of  New  York,  and  Fig.  212 


THE  QUATERNARY  PERIOD  337 

is  a  structure  section  across  it  showing  the  rock  terraces  and  the 
relations  of  the  various  rock  formations.  The  conditions  for  ice 
erosion  there  were  unusually  favorable,  because  the  ice,  in  its  great 
sweep  around  the  Adirondacks,  was  heavily  shod  with  hard  rock 
fragments  and  entered  the  deep  valley  by  striking  with  greatest 
force  against  the  soft  rocks  on  the  west  side.  The  soft  shales  were 
worn  back  more  than  the  harder  limestones,  while  the  very  hard 
pre-Cambrian  rocks  were  but  little  affected.  If  soft  shales  had 
made  up  the  valley  bottom,  ice  erosion  would  have  caused  consid- 
erable deepening,  as  was,  no  doubt,  the  case  in  the  valleys  of  the 
Finger  Lakes  region  of  western  New  York.  Even  in  places  so 
favorably  situated  as  those  just  mentioned  there  is  no  reason  to 
believe  that  ice  erosion  did  any  more  than  to  modify  the  profiles 
of  the  pre-Glacial  channels. 

It  is  also  a  singular  fact  that  glacial  deposits  left  by  one  ice 
sheet  may  actually  have  been  overridden  by  a  later  advance  of 
ice  with  little  erosion  of  even  such  soft  material.  This  probably 
happens  only  near  the  margin,  where  the  ice  is  rather  thin  and 
hence  would  not  be  expected  to  have  much  erosive  power. 

In  conclusion  we  may  say  that  while  many  comparatively 
small,  local  features  were  produced  by  ice  erosion,  the  major 
topographic  features  of  the  great  glaciated  area  were  practically 
unaffected  by  the  abrasive  effects  of  the  passing  ice  sheets. 

ICE  DEPOSITS 

The  vast  amount  of  debris  transported  by  the  great  ice  styeet 
was  carried  either  on  its  surface,  frozen  within  it,  or  pushed  along 
beneath  it.  It  was  heterogeneous  material  ranging  from  the  finest 
clay,  through  sand  and  gravel,  to  boulders  of  many  tons'  weight. 
The  deposition  of  these  materials  took  place  during  both  the 
advance  and  retreat  of  the  ice,  but  chiefly  during  its  retreat.  Most 
of  the  deposits  made  during  the  ice  advance  were  obliterated  by 
ice  erosion,  while  those  formed  at  the  time  of  the  retreat  have  been 
left  intact  except  for  the  small  amount  of  post-Glacial  erosion 
and  weathering.  The  term  " drift,"  applied  to  all  deposits  of  glacial 
origin,  was  given  at  a  time  when  they  were  regarded  as  flood  or 
iceberg  deposits.  Drift  covers  practically  all  of  the  glaciated  re- 
gion except  where  bare  rock  is  actually  exposed,  and  its  thickness 
is  very  variable,  ranging  from  nothing  to  some  hundreds  of  feet. 


338  HISTORICAL  GEOLOGY 

The  ice  sheet  could  advance  only  when  the  rate  of  motion  was 
greater  than  the  rate  of  melftng  of  the  ice  front,  and  vice  versa 
in  case  of  retreat.  Thus  it  is  true,  though  seemingly  paradoxical, 
to  assert  that  the  ice  was  constantly  flowing  southward  even 
while  the  ice  front  was  retreating  northward.  Whenever,  during 
the  great  general  retreat,  the  ice  front  remained  stationary  because 
the  forward  motion  was  just  counterbalanced  by  the  melting,  all 
the  ice  reaching  the  margin  of  the  glacier  dropped  its  load  to  build 
up  a  terminal  moraine.  Such  a  moraine  is  a  more  or  less  distinct 
ridge  of  low  hills  and  depressions  consisting  of  very  heterogeneous 
and  generally  unstratified  debris,  though  at  times  waters  emerging 
from  the  ice  caused  stratification.  The  depressions  are  usually 
called  kettle-holes.  The  so-called  great  terminal  moraine  marks 
the  southernmost  limit  of  the  ice  sheet,  and  is  wonderfully  well 
shown  by  the  ridge  of  low,  irregular  hills  extending  the  whole 
length  of  Long  Island.  It  is  also  more  or  less  clearly  traceable 
across  the  United  States,  where  it  marks  the  southernmost  limit  of 
glaciation.  Terminal  moraines  farther  northward  are  generally 
not  so  long  or  sharply  defined,  though  many  have  been  located 
and  described.  These  are  either  terminal  moraines  found  at  the 
southernmost  limits  of  ice  sheets  which  did  not  extend  as  far 
south  as  earlier  sheets,  or  recessional  moraines  formed  during  each 
considerable  pause  of  a  waning  or  northward  retreating  ice  sheet. 

When  the  ice  front  paused  for  a  considerable  time  upon  a  rather 
flat  surface,  the  debris-laden  streams  emerging  from  the  ice  formed 
what  is  called  an  overwash  plain  by  depositing  layers  of  sediment 
over  the  flat  surface.  An  excellent  illustration  of  such  an  overwash 
plain  is  all  of  that  part  of  Long  Island  lying  just  south  of  the  great 
terminal  moraine,  and  known  as  the  Jamaica  plain  toward  the  west. 

When  the  ice  front  extended  across  a  more  rugged  country, 
with  valleys  sloping  away  from  the  ice,  the  large  glacial  streams, 
heavy  laden  with  debris,  caused  more  or  less  deposition  of  materials 
on  the  valley  bottoms  often  for  many  miles  beyond  the  ice  front. 
Such  deposits,  known  as  valley  trains,  are  especially  well  developed 
along  many  of  the  larger  south-flowing  streams  of  the  glaciated 
area. 

Glacial  boulders  (erratics)  have  already  been  referred  to.  They 
are  simply  blocks  of  rock  or  boulders  from  the  top  of  the  ice  or 
within  it  which  have  been  left  strewn  over  the  country  as  a  result 
of  the  melting  of  the  ice.  They  vary  in  size  from  small  pebbles  to 


THE  QUATERNARY  PERIOD  339 

those  of  many  tons'  weight,  and  are  naturally  most  commonly 
derived  from  the  harder  and  more  resistant  rock  formations. 
Thus  erratics  from  the  Adirondack  Mountains  are  very  numerous 
from  central  to  southern  New  York.  Erratics  are  often  found  high 
up  on  the  mountains,  where  they  have  sometimes  been  left  stranded 
in  remarkably  balanced  positions. 

A  very  extensive  glacial  deposit,  called  the  ground  moraine,  is 
simply  the  heterogeneous,  typically  unstratified  debris  from  the 
bottom  of  the  ice  which  was  deposited,  sometimes  during  the  ice 
advance,  but  most  often  during  its  melting  and  retreat.  When  it 


Fig.  213 

Typical  drumlins  (side  view)  in  western  New  York.     (After  H.  L.  Fairchild, 
N.  Y.  State  Mus.,  Bui.  111.) 

is  mostly  very  fine  material  with  pebbles  or  boulders  scattered 
through  its  mass,  it  is  known  as  till  or  boulder  clay.  The  pebbles 
or  boulders  of  the  till  are  commonly  faceted  and  striated  as  a  result 
of  having  been  rubbed  against  underlying  rock  formations. 

Another  type  of  glacial  deposit  of  unusual  interest  is  the 
drumlin,  which  is  in  reality  only  a  special  form  of  ground  moraine 
material.  The  typical  drumlins  of  western  New  York,  Wisconsin, 
and  western  Massachusetts  are  low,  rounded  mounds  of  till  with 
elliptical  bases  and  steeper  slopes  on  the  north  sides.  Their  long 
axes  are  parallel  to  what  was  the  direction  of  ice  movement  (see 
Fig.  213).  In  height  they  rarely  exceed  200  feet,  being  most  often 
less  than  100  feet.  The  origin  of  the  drumlins  has  not  yet  been 
satisfactorily  determined,  though  it  is  known  that  they  formed  near 
the  margin  of  the  ice  either  by  the  erosion  of  an  earlier  drift  layer 
or  by  accumulation  beneath  the  ice  under  peculiarly  favorable 


340  HISTORICAL  GEOLOGY 

conditions,  as  perhaps  along  longitudinal  crevasses  or  fissures. 
Two  of  the  finest  and  most  extensive  exhibitions  of  drumlins  in 
the  world  are  in  New  York,  between  Syracuse  and  Rochester, 
and  in  eastern  Wisconsin,  where  thousands  of  them  rise  above  the 
general  level  of  the  plains  and  give  rise  to  a  unique  topography. 

Another  type  of  glacial  deposit  in  the  low  hill  form  is  the  kame, 
which,  in  contrast  with  the  drumlin,  always  consists  of  stratified 
drift.  Kames  are  seldom  as  much  as  200  feet  high,  and  typically 
they  have  nearly  circular  bases,  though  frequently  they  are  of 


Fig.  214 

A  group  of  kames  in  New  York  state.     (From  Norton's  "Elements 
of  Geology,"  by  permission  of  Ginn  and  Company,  Publishers.) 

very  irregular  shapes.  At  times  they  exist  as  isolated  hills  or  in 
small  groups  (Fig.  214),  while  often  they  are  associated  with  the 
unstratified  deposits  of  the  moraines.  When  grouped,  deep  depres- 
sions occur  between  the  hills  to  form  what  is  called  the  knob  and 
kettle  structure.  Kames  were  formed  at  or  near  the  margin  of  the 
retreating  ice,  and  so  are  found  in  all  parts  of  the  glaciated  area, 
but  more  especially  where  there  is  considerable  relief,  as  in  New 
York  and  New  England.  They  most  generally  are  located  in  valley 
bottoms,  but  sometimes  on  hillsides  or  even  hilltops.  They  are 
especially  abundant  along  the  line  of  the  great  terminal  moraine 
(e.g.  Long  Island)  and  along  the  lines  of  the  more  important 
recessional  moraines.  They  were  formed  as  deposits  by  debris- 
laden  streams  emerging  from  the  margin  of  the  ice,  the  water 


THE  QUATERNARY  PERIOD  341 

sometimes  having  risen  like  great  fountains  because  of  pressure. 
Such  deposits  are  now  actually  in  process  of  formation  along  the 
edge  of  the  great  Malaspina  glacier  of  Alaska. 

During  the  ice  retreat  glacial  lakes  were  numerous,  particularly 
where  the  north-sloping  valleys  were  dammed  by  the  ice  thus 
ponding  the  waters  in  the  valleys.  Some  materials  were  directly 
deposited  from  the  glacier  in  those  lakes,  but  more  was  brought 
in  by  debris-laden  streams  flowing  from  the  land  already  freed 
from  the  ice.  Such  glacial  lakes  and  their  deposits  were  common 
and  of  unusual  interest,  but  they  will  be  described  under  a  sub- 
sequent heading. 

In  conclusion  we  may  say  that  the  deposition  of  glacial  mate- 
rials, like  glacial  erosion,  has  not  changed  the  major  topographic 
features  of  the  glaciated  region.  The  general  tendency  of  ice 
deposits  has  been  to  fill,  or  partially  fill,  depressions  and  thus  to 
diminish  the  ruggedness  of  the  topography. 

THE  LOESS  DEPOSITS 

Loess  deposits  are  widespread  over  much  of  the  region  from 
eastern  Nebraska,  across  Iowa,  Illinois,  and  Indiana.  Its  distribu- 
tion is  pretty  largely  independent  of  topography.  Typically  it  is 
a  soft,  buff  to  yellowish-brown,  very  fine  grained,  sandy  clay  which 
seldom  shows  signs  of  stratification.  Its  thickness  usually  varies 
from  10  to  100  feet.  Where  eroded  or  cut  into,  the  loess  exhibits 
a  remarkable  tendency  to  stand  in  perpendicular  cliffs,  sometimes 
with  suggestions  of  a  sort  of  columnar  structure.  For  this  reason 
it  was  once  known  as  the  Bluff  formation.  It  is  remarkably  free 
from  coarse  materials,  except  for  certain  carbonate  of  lime  and 
oxide  of  iron  concretions  and  fossils,  the  latter  being  chiefly  shells 
of  land  Gastropods.  Most  of  the  loess  was  deposited  during  the 
lowan  Glacial  stage,  because  it  rests  upon  the  eroded  and  weath- 
ered surfaces  of  older  glacial  deposits  and  often  passes  under  the 
later  or  Wisconsin  deposits. 

The  question  as  to  whether  the  loess  was  of  aqueous  or  eolian 
origin  has  long  been  discussed.  "In  part  the  loess  seems  to  have 
been  washed  from  glacial  waste  and  spread  in  sluggish  glacial 
waters,  and  in  part  to  have  been  distributed  by  the  wind  from 
plains  of  aggrading  glacial  streams"  (W.  H.  Norton). 


342  HISTORICAL  GEOLOGY 

GREAT  LAKES  HISTORY 

The  Great  Lakes  certainly  did  not  exist  before  the  Ice  age,  but 
instead  the  depressions  in  that  region  were  occupied  by  stream 
channels.  During  the  very  long  erosion  period  from  the  Paleozoic 
to  the  Cenozoic,  no  lakes  of  any  consequence  could  have  persisted. 
Compared  with  such  an  immense  length  of  time  lakes  are,  at  most, 
only  ephemeral  features  of  the  earth's  surface  because  they  are  soon 
destroyed  either  by  being  filled  with  sediments,  or  by  having  their 
outlets  cut  down,  or  both.  Since  the  Great  Lakes  are  of  post- 
Glacial  origin  it  is,  then,  proper  to  ask  how  they  came  into  existence. 
During  pre-Glacial  time  broad  valleys  were  cut  out  along  belts  of 
weak  rock  in  the  Great  Lakes  region,  and  these  old  valleys,  to  a 
considerable  extent  at  least,  account  for  the  present  depressions, 
but  not  for  the  closed  lake  basins.  This  idea  of  pre-Glacial  stream 
valleys  is  not  at  all  opposed  by  the  fact  that  some  of  the  lake 
bottoms  are  now  well  below  sea  level,  because  there  has  been 
notable  subsidence  of  the  region  since  pre-Glacial  time.  The 
surface  of  Lake  Erie  is  573  feet,  and  its  deepest  point  369  feet, 
above  sea  level,  while  the  surface  of  Lake  Ontario  is  247  feet  above, 
and  its  deepest  point  is  491  feet  below,  sea  level.  The  greatest 
depth  (738  feet)  of  Lake  Ontario  is  well  toward  the  east  end  not 
far  from  the  south  shore,  and  if  we  consider  this  deep  place  as  due 
to  pre-Glacial  erosion,  we  ought  to  find  an  outlet  channel.  But 
no  such  outlet  channel  exists  because  the  whole  east  end,  at  least, 
of  the  lake  is  rock-rimmed.  As  Tarr  has  said:  "There  could 
hardly  be  a  valley  over  700  feet  deep  and  broad  enough  to  form  the 
continuation  of  the  pre-Glacial  Ontario  Valley,  which  is  so  com- 
pletely obscured  by  drift  that  not  the  least  trace  of  it  has  been 
found  on  the  surface."  l  To  assume  that  this  deep  part  of  the 
basin  was  formed  by  warping  of  the  land  is  not  borne  out  by  exam- 
ining the  exposed  strata  on  all  sides.  It  therefore  seems  quite 
certain  that  the  pre-Glacial  Ontario  depression  was  considerably 
deepened  by  ice  erosion.  The  conditions  were  very  favorable  for 
such  erosion  because  the  rocks  were  chiefly  soft  Ordovician  shales; 
because  the  ice  flowed  through  a  deep  pre-Glacial  valley;  and 
because  there  was  an  unusual  crowding  of  the  ice  into  this  valley 
due  to  pronounced  deflection  of  a  great  ice  current  around  the 
Adirondacks  on  the  west  side.  Strong  arguments  might  be  adduced 

1  R.  S.  Tarr:  Physical  Geography  of  New  York  State,  p.  235. 


THE  QUATERNARY  PERIOD 


343 


to  show  that  by  ice  erosion  portions,  at  least,  of  all  the  lake  basins 
were  appreciably  deepened.  Even  so,  however,  we  have  not  yet 
accounted  for  the  present  closed  basins.  Probably  the  two  most 
important  phenomena  which  have  contributed  to  the  formation  of 
the  closed  basins  of  the  Great  Lakes  are  (1)  the  great  drift  accumu- 
lations along  the  south  side  and  (2)  the  tilting  of  the  land  down- 
ward on  the  north  side  of  the  region.  The  deep  drift  deposits 
must  certainly  have  been  very  effective  in  damming  up  the  south 
or  southwest-flowing  pre-Glacial  streams  of  the  region.  A  great 


Fig.  215 

First  stage  in  the  history  of  the  Great  Lakes,  when  all  the 
rest  of  the  lake  basins  were  still  buried  under  the  ice. 
Shaded  portions  show  Lake  Chicago  on  the  left  and 
Lake  Maumee  on  the  right.  (After  Taylor  and  Leverett, 
redrawn  by  W.  J.  M.) 

dumping  ground  of  ice-transported  materials  from  the  north  was 
in  general  along  the  southern  side  of  the  Great  Lakes  and  south- 
ward. Late  in  the  Ice  age  the  land  on  the  northern  side  of  the 
Great  Lakes  region  was  lower  than  it  is  today,  as  proved  by  the 
tilted  character  of  certain  well-known  beaches  of  extinct  lakes 
(see  below).  Such  a  differential  tilting  or  warping  of  the  land  must 
have  helped  to  form  the  closed  basins  by  tending  to  stop  the  south- 
ward or  south  west  ward  drainage  from  the  region.  To  summarize, 
we  may  say  that  the  present  Great  Lakes  basins  are  due  to  a  com- 
bination of  factors,  the  more  important  of  which  were:  (1)  the 
formation  of  pre-Glacial  valleys  by  stream  erosion;  (2)  a  more  or 


344  HISTORICAL  GEOLOGY 

less  deepening  of  these  valleys  by  ice  erosion;  (3)  the  great  accumu- 
lation of  glacial  debris  along  the  southern  side  of  the  Lake  district; 
and  (4)  the  tilting  of  the  land  relatively  downward  toward  the 
north. 

We  are  now  ready  to  trace  out  the  principal  stages  in  the 
history  of  the  Great  Lakes  region  during  the  final  retreat  of  the 
great  ice  sheet.  When  the  ice  front  had  receded  far  enough  north- 
ward to  uncover  the  southern  end  of  Lake  Michigan,  and  an  area 


Fig.  216 

Lake  Whittlesey  stage  of  the  Great  Lakes  history,  when  the  eastern 
and  western  ice-margin  lakes  combined  with  outlet  past  Chicago. 
(After  Taylor  and  Leverett,  redrawn  by  W.  J.  M.) 

west  of  the  present  end  of  Lake  Erie,  small  lakes  were  formed 
against  the  ice  walls  (see  Fig.  215).  The  first  of  these  has  been 
called  Lake  Chicago,  which  drained  past  Chicago  through  the 
Illinois  River  and  into  the  Mississippi;  and  the  second,  Lake 
Maumee,  which  drained  southwestward  past  Fort  Wayne  through 
the  Wabash  River  and  thence  into  the  Ohio  and  Mississippi. 

At  a  later  stage  the  conditions  shown  on  map  Fig.  216  existed. 
Lake  Chicago  was  then  larger,  and  Lake  Maumee  had  expanded 
into  the  extensive  Lake  Whittlesey,  which  covered  nearly  all  of  the 
area  of  Lake  Erie  as  well  as  some  of  the  surrounding  country. 
Lake  Whittlesey  was  at  a  lower  level  than  the  former  Maumee,  and 
the  outlet  past  Fort  Wayne  ceased,  but  the  drainage  from  Whittle- 


THE  QUATERNARY  PERIOD 


345 


sey  was  westward  by  a  large  river  flowing  through  small  Lake 
Saginaw  and  into  Lake  Chicago,  which  latter  still  emptied  through 
the  Illinois  River. 

At  a  still  later  stage  (Fig.  217)  Lake  Saginaw  merged  with  the 
waters  of  the  Erie  Basin  to  form  the  large  Lake  Warren  which 
extended  along  the  ice  front  eastward  nearly  to  central  New  York. 
As  the  map  clearly  shows,  the  Finger  Lakes  Basins  of  New  York 
were  then  occupied  by  Warren  waters,  while  Niagara  Falls  were 


Fig.  217 

Glacial  Lake  Warren.  At  this  stage  the  discharge  of  the  lake  was  still  west- 
ward to  Lake  Chicago,  while  the  eastern  end  of  the  lake  covered  most  of 
the  Finger  Lakes  region  of  New  York.  (Modified  by  W.  J.  M.,  after  Taylor 
and  Leverett.) 

not  then  in  existence,  because  that  region  was  also  covered  by 
Lake  Warren.  Lake  Warren  continued  to  discharge  westward 
into  Lake  Chicago  and  the  Mississippi  River  until  a  very  late 
stage,  when  the  waters  had  worked  their  way  along  the  border  of 
the  Ontario  ice  lobe  into  the  Mohawk  Valley  of  New  York,  which 
was  then  occupied  by  a  large  glacial  lake  (held  up  by  the  Ontario 
ice  lobe  on  the  west  and  the  Champlain-Hudson  lobe  on  the  east), 
and  then  into  the  Hudson  Valley.  Thus,  for  the  first  time,  the 
Great  Lakes  drainage  passed  eastward  into  the  Atlantic  Ocean. 
This  great  volume  of  water  draining  eastward  was  often  in  the  form 
of  distinct  streams  with  the  ice  front  for  north  wall  and  the  high 


THE  QUATERNARY  PERIOD 


347 


land  of  the  Helderberg  escarpment  for  wall  on  the  south.  Many 
of  these  glacial  stream  channels,  often  high  up  on  the  hills  of 
central  to  western  New  York,  are  still  plainly  visible. 

By  successive  stages,  due  to  complete  removal  of  ice  from 
central  New  York,  and  a  draining  of  the  glacial  lake  in  the  Mohawk 
Valley,  the  waters  dropped  to  below  Warren  level  until  Lake  Iro- 


Fig.  219 

The  Algonquin-Iroquois  stage  of  the  Great  Lakes,  with  outlet  through  the 
Mohawk-Hudson  Valleys  of  New  York.  (After  Taylor,  courtesy  of  the 
New  York  State  Museum.) 

quois  was  formed  (see  Fig.  219).  The  old  beach  line  of  this  lake 
is  still  plainly  visible  in  New  York.  Lake  Iroquois  covered  some- 
what more  than  the  present  area  of  Lake  Ontario,  and  the  dis- 
tinctly lower  water  level  here  than  in  the  Erie  Basin  .allowed  the 
modern  Niagara  River  to  begin  its  history  by  flowing  northward 
over  the  limestone  plain  near  Buffalo.  Meantime  the  waters  of 
the  upper  lake  basins  had  merged  to  form  Lake  Algonquin,  which 
at  first  probably  discharged  past  Detroit  through  the  Erie  Basin 
and  into  Lake  Iroquois  by  way  of  Niagara  River.  Later,  however, 


348  HISTORICAL  GEOLOGY 

when  the  ice  had  withdrawn  a  little  farther  northward,  a  lower 
outlet  was  formed  through  the  Trent  River  by  which  Lake  Algon- 
quin drained  into  Lake  Iroquois.  The  old  Trent  River  channel  is 
now  higher  than  the  Detroit  outlet,  but  some  of  the  proofs  for  the 
former  Trent  outlet  are  as  follows:  (1)  The  presence  there  of  a 
large,  distinct  river  channel;  (2)  the  convergence  of  the  beaches 
toward  that  channel;  and  (3)  the  fact  that  the  land  was  then  con- 
siderably lower  on  the  north  or  northeast  side  of  Lakes  Ontario 
and  Erie  than  on  the  south  side.  For  example,  in  following  the 
old  Iroquois  beach  we  find  that  it  gradually  rises  to  higher  levels 
until  it  is  several  hundred  feet  higher  at  the  eas-t  than  near  the 
mouth  of  Niagara  River.  This  tilting  of  the  beach  has  been  due 
to  warping  of  the  land  since  the  lake  existed,  and  it  is  evident 
therefore  that  during  the  Algonquin-Iroquois  stage  the  Trent 
River  channel  was  lower  than  that  past  Detroit.  During  the 
Algonquin-Iroquois  stage  the  waters  of  all  the  Great  Lakes  region 
discharged  through  the  Mohawk-Hudson  valleys,  and  the  volume 
of  water  which  flowed  through  the  Mohawk  Valley  must  have 
been  as  great,  if  not  greater,  than  that  which  now  goes  over 
Niagara  Falls.  During  this  time  the  St.  Lawrence  Valley  was  still 
buried  under  ice. 

Still  later  the  ice  withdrew  enough  to  allow  the  Algonquin- 
Iroquois  waters  to  discharge  along  the  northern  base  of  the  Adiron- 
dacks  and  into  what  appears  to  have  been  ice-ponded  waters  in 
the  Champlain  Basin,  and  thence  into  the  Hudson  Valley.  The 
Mohawk  Valley  outlet  was  thus  abandoned. 

Finally  the  ice  withdrew  far  enough  to  free  the  St.  Lawrence 
Valley  when  the  waters  of  the  Great  Lakes  region  dropped  to  a 
still  lower  level,  bringing  about  the  Nipissing  Great  Lakes  stage 
(see  Fig.  220).  The  Nipissing  Lakes  found  a  low  outlet  through 
the  Ottawa  River  (then  free  from  ice)  and  into  the  Champlain 
arm  of  the  sea.  Post-Glacial  warping  of  the  land  brought  the  Great 
Lakes  region  into  the  present  condition,  but  this,  and  the  Cham- 
plain  subsidence,  being  really  post-Glacial  features,  will  be  de- 
scribed below. 


OTHER  EXISTING  LAKES  AND  THEIR  ORIGIN 

Counting  all,  from  the  smallest  to  the  largest,  there  are  within 
the  glaciated  area  of  North  America  tens  of  thousands  of  lakes, 


350  HISTORICAL  GEOLOGY 

and  these  constitute  one  of  the  most  striking  differences  between 
the  geography  of  the  present  and  that  of  pre-Glacial  time.  These 
lakes  are  widely  scattered,  though  in  the  United  States  they  are 
most  abundant  in  the  regions  of  greater  relief,  such  as  Maine,  New 
Hampshire,  New  York,  and  Minnesota,  because  lake  basins  were 
more  readily  formed  by  drift  dams  across  the  deeper  pre-Glacial 
valleys  of  those  regions. 

It  is  well  known  that  most  of  the  larger  lakes,  especially  those 
of  the  linear  type,  occupy  portions  of  pre-Glacial  stream  channels. 
All  the  existing  lakes  are  due,  either  directly  or  indirectly,  to 
glacial  action.  Among  the  ways  by  which  such  bodies  of  water 
may  be  formed  are  these:  (1)  by  building  dams  of  glacial  drift 
across  old  river  channels;  (2)  by  ice  erosion;  and  (3)  by  accumu- 
lation of  water  in  the  numerous  depressions  which  were  formed  by 
irregular  deposition  of  the  drift  (kettle-holes,  etc.).  Hundreds  of 
small  lakes,  often  not  more  than  mere  pools  in  size,  belong  to  the 
last  named  type,  while  very  many  of  the  large  and  small  lakes  are 
due  chiefly  to  the  existence  of  drift  dams.  Certain  lakes  in  south- 
eastern Canada  and  elsewhere  appear  to  occupy  rock  basins  scoured 
out  by  ice  erosion. 

In  considering  the  origin  of  glacial  lakes,  the  so-called  Finger 
Lakes  of  central-western  New  York  deserve  special  mention.  All 
are  agreed  that  the  lakes  of  this  remarkable  group  occupy  pre- 
Glacial  valleys,  most  of  which,  at  least,  contained  north-flowing 
streams.  These  lakes  have  dams  of  glacial  drift  across  their  lower 
(north)  ends,  and  the  dams  have  been  important  factors  in  the 
formation  of  the  lakes,  being  in  some  cases  perhaps  the  sole  cause. 
But  in  the  cases  of  the  two  largest  lakes  —  Seneca  and  Cayuga  — 
there  is  strong  evidence,  from  the  hanging  valley  character  of  the 
tributaries,  that  the  pre-Glacial  valleys  were  notably  deepened 
by  ice  erosion. 

The  presence  of  Lake  Champlain  is  due  principally  to  a  com- 
bination of  factors,  including  late  elevation  of  the  land,  with  greater 
uplift  on  the  north;  heavy  glacial  accumulations  toward  the  north; 
and  possibly  some  deepening  as  a  result  of  ice  erosion. 

In  the  basin  of  Lake  George  there  was  a  pre-Glacial  divide 
where  the  " Narrows"  are  now  located,  and  this  divide  appears 
to  have  been  considerably  lowered  by  ice  erosion  when  part  of 
the  Champlain  ice  lobe  ploughed  its  way  through  the  deep,  narrow 
valley.  The  waters  are  now  held  in  by  drift  dams  at  each  end. 


THE  QUATERNARY  PERIOD  351 

Well  within  the  glaciated  region  of  the  interior  of  the  continent 
the  history  of  Lake  Winnipeg  is  of  special  interest,  but  since  this 
lake  is  merely  a  remnant  of  a  former  much  larger  body  of  water,  it 
will  be  described  in  connection  with  extinct  glacial  lakes. 


EXTINCT  GLACIAL  LAKES 

Thousands  of  extinct  glacial  lakes  are  known  to  be  scattered 
over  the  glaciated  area.  Some  of  these  existed  only  during  the  time 
of  the  ice  retreat,  while  others  persisted  for  a  greater  or  lesser 
length  of  time  after  the  Ice  age.  Lakes  Warren,  Iroquois,  etc., 
already  described,  were  fine  examples  of  the  first  type.  North- 
sloping  valleys  were  particularly  favorable  for  the  development  of 
glacial  lakes  during  the  retreat  of  the  ice,  because  the  ice  front 
always  acted  as  a  dam  across  such  valleys,  thus  causing  the 
waters  to  become  ponded.  Among  the  best  criteria  for  the  recog- 
nition of  these  extinct  glacial  lakes  are  typical,  flat-topped,  delta 
deposits  formed  by  inflowing  streams  and  distinct  beaches. 

A  very  fine  example  of  many  large,  wholly  extinct  glacial  lakes 
is  Black  Lake,  which  occupied  a  good  portion  of  the  Black  River 
Valley  on  the  western  side  of  the  Adirondacks  in  New  York.  This 
body  of  water,  small  at  first,  was  formed  by  ponding  the  waters 
in  the  valley  by  the  waning  (northward  retreating)  ice  lobe.  Its 
earlier  discharge  was  southward.  Further  retreat  of  the  ice  front 
allowed  Black  Lake  to  expand  greatly  until  it  had  a  width  of  from 
5  to  10  miles  and  a  length  of  from  25  to  30  miles.  Finally  the  ice 
withdrew  far  enough  northward  to  permit  a  discharge  of  the  lake 
waters  northward  and  the  lake  soon  drained  away  entirely.  A 
great  delta  deposit,  formed  by  the  coalescence  of  smaller  deltas 
produced  by  the  streams  which  drained  into  Black  Lake  from  the 
Adirondack  Mountains,  may  now  be  seen  in  a  remarkable  state  of 
preservation  on  the  west  side  of  the  valley  (Fig.  212).  It  is  some 
30  miles  long,  several  miles  wide,  very  flat-topped  except  where 
trenched  by  post-Glacial  streams,  presents  a  steep  front  toward 
the  west,  and  shows  a  depth  of  from  200  to  250  feet  along  its 
western  edge. 

A  fine  example  of  a  very  large  glacial  lake  in  the  interior  of 
North  America,  and  now  represented  only  by  remnants  (e.g. 
Lake  Winnipeg),  has  been  called  Lake  Agassiz  in  honor  of  the  dis- 
coverer of  the  fact  of  the  Quaternary  Ice  age.  This  lake,  fully 


352 


HISTORICAL  GEOLOGY 


700  miles  long  and  several  hundred  miles  wide,  extended  over  the 
whole  valley  of  the  Red  River  of  the  North  in  North  Dakota  and 
Minnesota,  and  northward  over  much  of  Manitoba.  It  covered 
a  larger  area  than  the  combined  Great  Lakes.  Its  water  was 
held  up  by  the  united  fronts  of  the  Kewatin  and  Labradorean 
ice  sheets  as  they  retreated  northward.  Its  outlet  was  southward 
through  the  Minnesota  and  Mississippi  rivers  until  the  ice 


Fig.  221 

Sketch  map  of  central  New  York,  showing  the  relation  of  the  pre-Glacial 
drainage  to  that  of  the  present.  Pre-Glacial  drainage  shown  by  dotted 
lines  only  where  essentially  different  from  existing  streams.  (By  W.  J.  M., 
based  on  work  by  A.  P.  Brigham.) 

melted  back  (northward)  far  enough  to  open  the  outlet  by  way  of 
Nelson  River  to  Hudson  Bay,  when  the  great  body  of  water  was 
rapidly  lowered,  leaving  only  the  present-day  remnants,  principally 
Lake  Winnipeg.  The  soil  of  this  smooth  old  lake  bed  is  wonder- 
fully rich. 

DRAINAGE  CHANGES  DUE  TO  GLACIATION 

In  addition  to  its  lakes,  the  glaciated  area  is  also  characterized 
by  numerous  gorges  and  waterfalls,  which  are  largely  due  to  glacia- 
tion.  As  a  result  of  the  very  long  time  of  pre-Glacial  erosion,  it 


THE  QUATERNARY  PERIOD 


353 


is  certain  that  typical,  steep-sided,  narrow  gorges,  as  well  as 
waterfalls,  must  have  been  very  uncommon,  if  present  at  all. 
Like  lakes,  such  fea- 
tures are  ephemeral, 
because,  under  our 
conditions  of  climate, 
gorges  soon  (geolog- 
ically) widen  at  the 
top,  and  waterfalls 
disappear  by  retreat 
or  by  wearing  away 
the  hard  rock  which 
causes  them. 

Changes  of  stream 
courses  are  also  nu- 
merous in  many  parts 
of  the  glaciated  ter- 
ritory. It  is  the  pres- 
ent purpose  to  de- 
scribe only  a  few 
typical,  well-studied 
cases  of  such  stream 
changes. 

From  the  stand- 
point of  both  geology 
and  human  history, 
the  gorge  at  Little 
Falls  (on  the  New 
York  Central  R.  R.) 
in  central  New  York 


PREGLACIAL     STREAMS 


is  the  most  impor- 
tant in  that  state. 
Before  the  Ice  age 
there  was  a  divide 
instead  of  a  gorge 
several  hundred  feet 
above  the  present 

river  level.  The  Mohawk  River  flowed  eastward,  and  the  now 
extinct  Rome  Kiver  flowed  westward  from  that  divide  (see  Fig. 
221).  During  the  Algonquin-Iroquois  stage  of  the  Great  Lakes 


Fig.  222 

Sketch  map  of  the  southeastern  Adirondack 
region,  showing  the  relation  of  the  pre-Glacial 
drainage  to  that  of  the  present.  Pre-Glacial 
courses  shown  by  dotted  lines  only  where  es- 
sentially different  from  present  streams.  (After 
W.  J.  Miller,  Bui.  Geol.  Soc.  Amer.,  vol.  22.) 


354 


HISTORICAL  GEOLOGY 


history,  those  lakes  discharged  through  the  Mohawk  Valley  and 
across  the  Little  Falls  divide.    It  was  the  passage  of  this  great 

volume  of  water  over  the  di- 
vide which  caused  the  cutting 
of  most  of  the  gorge  as  we  now 
see  it,  except  for  the  narrow 
trench  in  the  hard,  low-lying 
rock,  which  is  no  doubt  due 
to  post-Glacial  erosion.  Dur- 
ing the  gorge  cutting,  ag- 
gradation (building  up  by 
sediments)  of  the  valley  bot- 
tom took  place  westward  from 
Little  Falls,  so  that  the  drain- 
age from  Rome,  N.  Y.,  was 
able  to  continue  eastward 
even  after  the  disappearance 
of  Lake  Iroquois.  Thus  we 
have  here  an  excellent  illus- 
tration of  exact  reversal  of 
drainage  due  to  glaciation, 
and  by  this  means  the  upper 
waters  of  the  present  Mohawk 
River  were  added  to  what  was 
the  pre-Glacial  Mohawk. 

In  the  southeastern  Adi- 
rondack Mountains  certain 
important  principles  of  drain- 
age changes  due  to  glaciation 
are  illustrated  by  the  upper 
waters  of  the  Hudson  River. 
The  accompanying  sketch  map 
(Fig.  222)  gives  an  idea  of  the 
changes.  Near  Warrensburg 
the  Hudson  River  was  de- 
flected westward  from  its  pre- 
Glacial  channel  because  of  the 
presence  of  a  lobe  of  the  wan- 
ing ice  sheet  in  the  Lake 
George  depression.  At  Corinth 


Fig.  223 

Sketch  map  of  the  Niagara  River  gorge. 
(Modified  after  Gilbert,  from  Nor- 
ton's   "Elements   of   Geology,"    by 
permission  of  Ginn  and  Company, 
,  Publishers.) 


THE  QUATERNARY  PERIOD 


355 


and  Northampton,  respectively,  the  Hudson  and  Sacandaga  rivers 
show  remarkable  eastward  deflections  instead  of  following  broad, 
deep  pre-Glacial  valleys  southward  into  the  Mohawk  Valley. 
These  deflections  were  caused 
by  heavy  morainic  deposits 
acting  as  dams  across  the 
valleys  south  of  Corinth  and 
Northampton. 

The  world-famous  Niagara 
Falls  and  gorge  are  wholly 
post-Glacial  in  origin.  After 
plunging  167  feet  at  the  falls, 
the  river  rushes  for  7  miles 
through  the  gorge,  whose  depth 
is  between  200  and  300  feet. 
When  the  glacial  waters  in  the 
eastern  Great  Lakes  region 
had  dropped  to  the  Iroquois 
level,  the  Niagara  limestone 
terrace  in  the  vicinity  of 
Buffalo  and  with  steep  escarp- 
ment or  northern  front  at 
Lewiston  and  Queenston, 
ceased  to  be  covered  with  lake 
water,  and  the  Niagara  River 
came  into  existence  by  flowing 
northward  over  this  limestone 
plain.  The  river  first  plunged 
over  the  escarpment  at  Lewis- 
ton,  thus  inaugurating  the  falls  Fig.  224 
there.  Since  that  time  the  Pre-Glacial  drainage  of  the  upper 

Ohio  River  Basin.    (After  Chamber- 


lin  and  Leverett,  from  Norton's 
"  Elements  of  Geology,"  by  permis- 
sion of  Ginn  and  Company,  Pub- 
lishers.) 


falls  have  receded  the  7  miles 

up    stream    to    their   present 

position.    Soft  shales  underlie 

the  layer  of    harder  Niagara 

limestone,  and  the  recession  of 

the  falls  has  clearly  been  caused  by  the  breaking  off  of  blocks  of 

limestone  due  to  undermining  of  the  soft  shales.     A  glance  at  the 

map  (Fig.  223)  will  show  that  the  gorge  development  is  really 

taking  place  on  the  Horseshoe  Falls  side,  where  the  volume  of 


356 


HISTORICAL  GEOLOGY 


water  is  much  greater,  and  that  in  a  short  time,  geologically  con- 
sidered, the  American  Falls  will  be  dry. 

The  drainage  of  the  upper  Ohio  River  Basin  has  been  well-nigh 
revolutionized  as  a  result  of  glaciation.  By  comparing  the  pre- 
Glacial  drainage  map  (Fig.  224)  with  one  showing  present-day 
drainage,  the  principal  changes  will  be  readily  understood.  The 
pre-Glacial  upper  Ohio  flowed  northward  from  Beaver,  Pennsyl- 
vania, instead  of  southward,  as 
at  present,  and,  between  Beaver 
and  Sharon,  the  direction  of  pre- 
Glacial  drainage  has  been  ex- 
actly reversed.  Also,  all  of  what 
is  now  known  as  the  drainage 
area  of  the  upper  Allegheny 
River  passed  northward  through 
two  pre-Glacial  streams.  The 
drainage  changes  were  caused  by 
ice  occupancy  and  deposition  of 
heavy  drift  across  the  north- 
western portion  of  Pennsylvania. 
Another  well-studied  example 
of  important  drainage  change  is 
shown  by  the  accompanying 
map  (Fig.  225)  of  part  of  north- 
ern Illinois.  The  pre-Glacial 
Rock  River  flowed  southward 
into  the  Illinois  River,  instead 
of  southwestward  into  the  Mis- 
sissippi as  at  present. 

Even  such  large  rivers  as  the 


Fig.  225 

Pre-Glacial  drainage  (dotted  lines) 
of  a  part  of  northwestern  Illinois. 
(Modified  after  Leverett.) 

Mississippi   and  Missouri  were 

sometimes  notably  shifted  out  of  their  pre-Glacial  channels  by 
the  invasion  of  the  ice  sheets.  Thus  the  Missouri  River,  which 
formerly  followed  what  is  now  the  James  River  Valley  in  eastern 
South  Dakota,  was  forced  many  miles  westward  to  its  present 
course  across  the  state. 

The  above  cited  cases  are  sufficient  to  illustrate  the  general 
principles  of  drainage  modifications  due  to  glaciation,  the  two 
chief  factors  having  been  (1)  actual  presence  of  the  ice  or  (2) 
heavy  drift  filling  in  pre-Glacial  valleys. 


THE  QUATERNARY  PERIOD  357 

ADVANTAGES  AND  DISADVANTAGES  OF  GLACIATION 

Advantages.  —  As  a  result  of  late  Tertiary  stream  dissection, 
much  of  what  is  now  the  glaciated  area  of  the  United  States  had 
been  converted  into  a  fairly  rugged  country.  Because  of  the 
heavy  accumulations  of  drift,  chiefly  in  the  depressions,  this 
ruggedness  was  greatly  diminished  and,  in  fact,  many  districts 
were  actually  converted  into  almost  featureless  plains.  Old 
lake  beds  (e.g.  that  of  Lake  Agassiz)  also  are  usually  very 
smooth.  Thus,  agricultural  pursuits,  transportation,  and  travel 
have  been  made  easier. 

Over  very  extensive  areas,  such  as  the  upper  Mississippi 
Valley,  the  soils  have  been  made  deeper  and  richer  on  the  average 
because  the  pre-Glacial  soils  were  not  only  comparatively  thin  on 
the  numerous  hillsides,  but  also  they  were  sandy  or  clayey  residual 
materials  from  which  much  of  the  rich  (soluble)  mineral  plant 
foods  had  been  washed  out.  The  glacial  drift  soils  are  usually 
more  uniformly  deep  and  consist  of  finely  ground  rocks  of  many 
kinds  still  rich  in  the  soluble  plant  foods. 

Water-power  facilities  have  been  vastly  increased  because  of  the 
development  of  thousands  of  waterfalls,  rapids,  and  lakes.  Pre- 
Glacial  streams  were  mostly  graded  and  hence  without  waterfalls 
or  rapids,  while  pre-Glacial  lakes  were  almost  entirely  absent. 
Lakes,  by  acting  as  reservoirs,  help  much  in  causing  a  more  uniform 
flow  of  streams.  In  many  places  such  reservoir  effect  is  furthered 
by  artificially  increasing  the  heights  of  the  natural  dams,  as  e.g. 
in  the  Adirondacks.  Also  many  large  reservoirs  can  easily  be  con- 
structed at  comparatively  little  expense  by  restoring  dams  of 
extinct  lakes. 

Large  lakes  afford  cheap  transportation  facilities,  and  often 
have  a  tempering  influence  upon  the  climate.  Many  lakes  fur- 
nish abundant  water  supplies  for  towns  and  cities,  as  well  as 
more  or  less  fish  for  food. 

The  benefit  of  lakes,  waterfalls,  gorges,  etc.,  from  the  aesthetic 
or  scenic  standpoint  would  be  difficult  to  overestimate. 

Drift  deposits  are  often  used,  e.g.  clays,  for  the  manufacture 
of  brick,  tile,  etc.,  and  sand  and  gravel  for  various  construction 
purposes. 

Disadvantages.  —  In  some  cases  the  earth's  surface  has  been 
increased  in  ruggedness  by  the  drift  accumulations,  especially  in 


358  HISTORICAL  GEOLOGY 

extensive  kame-moraine  areas,  thus  hindering  agriculture,  trans- 
portation, and  travel. 

In  many  places,  as  in  parts  of  New  England,  New  York,  and 
eastern  Canada,  the  cultivation  of  the  soil  has  been  made  difficult 
because  of  the  numerous  glacial  boulders  it  contains.  In  these 
same  regions  many  of  the  old  lake  or  other  deposits  are  too  sandy 
or  gravelly  to  be  very  fertile. 

Large  areas  now  covered  by  lake  waters  would  make  valuable 
farming  land.  This  is  particularly  true  of  the  Great  Lakes. 

All  things  considered,  it  seems  certain  that  the  advantages  due 
to  glaciation  are  notably  greater  than  the  disadvantages. 

DURATION  OF  THE  GLACIAL  EPOCH 

According  to  Chamberlin  and  Salisbury,  the  most  important 
criteria  for  estimating  the  duration  of  the  Glacial  epoch  include: 
"  (1)  the  amount  of  erosion  of  the  drift;  (2)  the  depth  of  leaching, 
weathering,  and  decomposition  of  its  materials;  (3)  the  amount  of 
vegetable  growth  in  interglacial  intervals;  (4)  the  climatic  changes 
indicated  by  interglacial  and  glacial  floras  and  faunas;  (5)  the 
times  needful  for  the  migration  of  faunas  and  floras,  particularly 
certain  plants  whose  means  of  migration  are  very  limited;  (6)  the 
time  required  for  advances  and  retreats  of  the  ice;  and  some 
others."  A  few  of  these,  as  the  first,  are  subject  to  direct  measure- 
ment, but  most  of  them  are  matters  of  judgment. 

The  average  of  the  estimates  of  five  glacial  geologists  who 
have  most  studied  the  data  is  shown  in  the  following  table : 

From  the  Late  Wisconsin  to  the  present 1  time  unit. 

From  the  lowan  to  the  present 3  to  5  time  units. 

From  the  Illinoian  to  the  present 7  to  9  time  units. 

From  the  Kansan  to  the  present 15  to  17  time  units. 

From  the  Sub-Aftonian  (Jerseyan)  to  the  present  ....  X  time  units.1 

"  After  carefully  considering  many  points,  these  same  authors 
(Chamberlin  and  Salisbury)  offer  the  following  table  accompanied 

Climax  of  the  (Late)  Wisconsin 20,000  to  80,000  years  ago. 

Climax  of  the  lowan 60,000  to  400,000  years  ago. 

Climax  of  the  Illinoian 140,000  to  720,000  years  ago. 

Climax  of  the  Kansan 300,000  to  1,360,000  years  ago. 

Climax  of  the  Sub-Aftonian  (Jerseyan) Y  to  Z  years  ago. 

1  Chamberlin  and  Salisbury:  College  Geology,  pp.  890-891. 


THE  QUATERNARY  PERIOD  359 

by  the  statement  that  "  little  value  is  to  be  placed  on  estimates  of 
this  kind,  except  as  a  means  for  developing  a  conception  of  the 
order  of  magnitude  of  the  time  involved."  l 

LENGTH  OF  TIME  SINCE  THE  GLACIAL  EPOCH 

Estimates  of  the  length  of  time  since  the  close  of  the  Ice  age 
are  perhaps  more  satisfactory,  though  it  must  be  remembered  that 
the  close  of  the  Ice  age  was  not  the  same  for  all  places.  The  ice 
retreated  northward  very  slowly  and  when,  for  example,  southern 
New  York  was  free  from  the  ice,  northern  New  York  was  still 
occupied  by  the  glacier.  The  best  estimates  of  the  length  of 
time  since  the  close  of  the  Ice  age  are  based  upon  the  rate  of 
recession  of  Niagara  Falls.  We  have  learned  that  Niagara  River 
began  its  work  about  the  time  the  glacial  waters  in  the  Erie-On- 
tario basins  dropped  to  the  Iroquois  level,  and  that  the  falls  were 
first  formed  by  the  plunging  of  the  river  over  the  limestone  es- 
carpment at  Lewiston.  Studies  based  upon  actual  surveys,  draw- 
ings, daguerreotypes,  photographs,  etc.,  made  between  the  years 
1842  and  1905,  have  shown  that  the  Horseshoe  Fall  had  receded 
about  5  feet  a  year,  while  the  American  Fall,  between  1827  and 
1905,  had  receded  about  3  inches  a  year.  Thus  the  gorge  cutting 
is  clearly  taking  place  on  the  Canadian  side.  The  length  of  the 
gorge  is  7  miles,  and  if  we  consider  the  rate  of  recession  to  have 
been  always  5  feet  a  year,  the  length  of  time  necessary  to  cut  the 
gorge  would  be  something  over  7000  years.  But  the  problem  is 
not  so  simple,  since  we  know  that  at  the  time  of,  or  shortly  after, 
the  beginning  of  the  river,  the  upper  lakes  drained  out  through 
the  Trent  River,  and  then  still  later  through  the  Ottawa  River. 
So  it  is  evident  that,  for  a  good  part  of  the  time  since  the  ice 
retreated  from  the  Niagara  region,  the  volume  of  water  passing 
over  the  falls  was  notably  diminished,  and  hence  the  length  of 
time  for  the  gorge  cutting  increased.  The  best  estimates  for  the 
length  of  time  since  the  ice  retreated  from  the  Niagara  region 
vary  from  7000  to  50,000  years,  an  average  being  about  25,000 
years.  In  a  similar  way,  the  time  based  upon  the  recession  of  St. 
Anthony's  Falls,  Minnesota,  ranges  from  about  10,000  to  16,000 

1  Obviously,  the  determination  of  the  number  of  years  equivalent  to  one 
time  unit  involves  the  determination  of  the  time  since  the  disappearance  of 
the  last  ice  sheet,  and  this  is  discussed  under  the  next  heading. 


360  HISTORICAL  GEOLOGY 

years.  While  closer  estimates  are  practically  impossible,  it  is  at 
least  certain  that  the  time  since  the  Ice  age  is  far  less  than  its 
duration,  and  that,  for  the  region  of  the  northern  United  States, 
the  final  ice  retreat  occurred  only  a  very  short  (geological)  time 
ago. 

When  we  consider  the  slight  amount  of  weathering  and  erosion 
of  the  latest  glacial  drift,  we  are  also  forced  to  conclude  that  the 
time  since  the  close  of  the  Ice  age  in  the  United  States  is  to  be 
measured  by  only  some  thousands  of  years.  Thus  kames,  drumlins, 
extinct  lake  deltas,  and  moraines  with  their  kettle-holes,  have 
generally  been  very  little  affected  by  erosion  since  their  formation. 

In  order  to  determine  the  number  of  years  ago  since  the  last 
(Wisconsin)  ice  sheet  reached  its  climax,  it  is  further  necessary 
to  know  how  long  it  took  this  ice  sheet  to  recede  from  its  southern- 
most limit  to  Niagara  Falls,  or  about  600  miles.1  If  we  allow  for  a 
rate  of  retreat  of  100  to  200  feet  per  day,  it  required  about  15,000 
to  30,000  years  for  the  retreat  to  Niagara.  Combining  these 
figures  with  those  above  given  for  the  time  since  the  inauguration 
of  Niagara  Falls,  we  get  some  idea  of  the  time  since  the  last  ice 
sheet  reached  its  climax,  or  about  22,000  to  80,000  years  ago. 

CAUSE  OF  THE  GLACIATION 

The  cause  of  the  glaciation  has  been  a  very  perplexing  problem. 
Various  hypotheses,  often  of  widely  different  character,  have  been 
offered  by  way  of  explanation,  but  there  is  nothing  like  general 
agreement  on  the  subject.  We  have  here  a  fine  illustration  of  the 
difference  between  "fact"  and  "hypothesis"  which  the  student  of 
natural  science  must  always  keep  clearly  in  mind.  Thus,  the  fact 
of  the  Glacial  epoch  (including  much  of  its  history)  is  conclusively 
established,  but  the  cause  of  the  glaciation  is  a  matter  concerning 
which  we  have  only  hypotheses  or  speculations. 

In  this  elementary  work  we  can  do  no  more  than  suggest  several 
of  the  leading  hypotheses.  Those  further  interested  in  the  subject 
are  referred  to  special  articles  and  larger  general  works,  particu- 
larly Chamberlin  and  Salisbury's  "  Geology,"  Vol.  3.  One  point  to 
be  borne  in  mind  is  that  no  hypothesis  is  required  to  account  for 
an  average  yearly  temperature  of  more  than  10  or  possibly  15  de- 

1  It  should  be  remembered  that  the  latest  or  Wisconsin  ice  did  not  extend 
as  far  south  as  certain  earlier  ice  sheets. 


THE  QUATERNARY  PERIOD  361 

grees  lower  than  at  present  over  the  glaciated  area  in  order  to 
have  brought  on  the  Ice  age. 

A  Geologic  (elevation)  Hypothesis.  —  As  we  have  already 
pointed  out,  the  evidence,  chiefly  from  the  submerged  river  chan- 
nels along  the  Atlantic  Coast,  clearly  indicates  greater  altitude  of 
northeastern  North  America  late  in  the  Tertiary  and  probably 
also  in  the  early  Quaternary.  An  altitude  of  from  4000  to  5000 
feet  greater  than  now  has  been  claimed  for  this  region.  Since  it  is 
well  known  that  the  temperature  becomes  lower  with  increasing 
altitude  (one  degree  for  about  300  feet),  it  has  been  argued  that 
the  greater  altitude  of  the  glaciated  area  was  in  itself  sufficient 
cause  for  the  glaciation.  "Northern  elevation  produced  ice- 
accumulation;  ice-accumulation  by  weight  produced  subsidence; 
subsidence  produced  moderation  of  temperature  and  melting  of 
ice;  and  this  last  by  lightening  of  load  produced  re-elevation" 
(J.  Le  Conte).  It  is  not  necessary  to  assume  that  maximum  eleva- 
tion and  ice-accumulation  were  coincident,  because  an  effect  often 
lags  behind  its  cause.  This  northern  elevation  also  is  believed  to 
have  sufficiently  upraised  the  northern  ocean  basins  to  cut  off 
warm  currents,  like  the  Gulf  Stream,  thereby  depriving  the  north- 
ern lands  of  such  warming  influences. 

It  has  been  urged  against  this  hypothesis  that  there  is  no  posi- 
tive evidence  for  nearly  as  much  as  4000  to  5000  feet  of  elevation 
of  the  glaciated  region ;  that  it  is  not  at  all  proved  that  the  northern 
elevation  occurred  at  the  proper  time  to  produce  glaciation;  and 
that  the  only  way  glacial  and  interglacial  stages  could  be  accounted 
for  would  be  by  the  unreasonable  assumption  of  repeated  elevation 
and  subsidence  corresponding  to  each  advance  and  retreat  of  the 
ice. 

Croll's  Astronomic  Hypothesis.1  —  According  to  Croll,  as 
excellently  interpreted  by  Le  Conte,  the  glaciation  was  caused  by 
"the  combined  influence  of  precession  of  the  equinoxes  and  secular 
changes  in  the  eccentricity  of  the  earth's  orbit.  By  the  former 
—  viz.,  precession  —  winter,  which  in  the  northern  hemisphere 
occurs  now  when  the  earth  is  nearest  the  sun  (perihelion),  is 
gradually  in  10,500  years  brought  round  so  as  to  occur  when  the 
earth  is  farthest  off  from  the  sun  (aphelion)  (Fig.  226).  The  effect 
of  this,  it  is  claimed,  would  be  to  make  longer  and  colder  winters, 

1  For  a  fuller  statement  of  this  hypothesis  see  Croll's  Climate  and  Time 
in  their  Geological  Relations,  1890. 


362 


HISTORICAL  GEOLOGY 


and  shorter  but  hotter  summers  in  the  northern  hemisphere, 
such  as  now  occur  in  the  Antarctic  regions.  By  the  latter  —  viz., 
increasing  eccentricity  (which  forms  a  much  longer  cycle)  —  these 
effects,  which  are  now  small  on  account  of  the  nearly  circular  form 
of  the  earth's  orbit,  would  become  very  great.  At  the  time  of  great- 
est eccentricity,  the  earth  would  be  14,000,000  miles  farther  off 
from  the  sun  in  winter  than  in  summer,  the  winter  would  be 
twenty-two  days  longer  and  20°  colder,  and  the  summers  twenty- 
two  days  shorter, 
but  much  hotter 
than  now.  .  .  . 
Now,  according  to 
Croll,  the  coinci- 
dence of  aphelion 
winter,  with  a 
period  of  greatest 
eccentricity  pro- 
duces a  glacial 
climate."  l 

As  a  result  of 
the  astronomic  re- 
lations, Croll  held 
that  the  heat 


Fig.  226 

Diagram  showing  effect  of  Precession:  A,  present 
condition;  B,  condition  10,500  years  hence.  Ec- 
centricity much  exaggerated.  (After  Le  Conte's 
"Geology,"  permission  of  D.  Appleton  and  Com- 
pany.) 


equator,  with  the 
trade  winds  zone, 
must  have  been  shifted  farther  away  from  the  glaciated  hemi- 
sphere with  consequent  shifting  of  direction  of  warm  ocean  cur- 
rents. Thus,  during  the  Quaternary  Glacial  epoch,  the  Gulf 
Stream  must  have  been  diverted  southward  by  the  eastern  point 
of  South  America. 

According  to  Croll's  hypothesis  (1)  there  must  have  been  many 
Glacial  epochs  during  the  earth's  history;  (2)  alternations  of  cold 
and  warm  stages  (seven  or  eight)  must  have  occurred  during  the 
Glacial  epoch;  (3)  these  cold  and  warm  stages  alternated  between 
northern  and  southern  hemispheres;  and  (4)  the  Quaternary 
Glacial  epoch  in  the  northern  hemisphere  began  240,000  years 
ago,  lasted  160,000  years,  and  declined  80,000  (or  possibly  60,000) 
years  ago. 

At  present  we  have  positive  evidence  for  five  or  six  times  of 
1  J.  Le  Conte:  Elements  of  Geology,  5th  ed.,  pp.  613-614. 


THE  QUATERNARY  PERIOD  363 

glaciation  during  geologic  history  and  still  more  may  be  discovered.1 
Also  it  has  been  proved  that  there  were  five,  and  probably  six, 
ice  advances  and  retreats  corresponding  to  colder  and  warmer 
stages  during  the  Quaternary  Glacial  epoch.  As  regards  the  dura- 
tion of  this  Ice  age  and  the  time  since  its  close,  it  seems  impossible 
to  imagine  seven  or  eight  advances  and  retreats  of  the  ice  within 
160,000  years  unless  we  postulate  rates  of  advance  and  retreat 
much  greater  than  studies  of  existing  glaciers  show.  Also  the  best 
geological  evidence  does  not  place  the  close  of  the  Ice  age  so  far 
away  as  60,000  to  80,000  years.  One  of  the  most  serious  objections 
to  Croll's  hypothesis  is  the  fact  that,  during  the  Permian  period, 
there  was  widespread  glaciation  in  comparatively  low  latitudes 
(20°  to  35°)  either  side  of  the  equator. 

Chamberlin's  Atmospheric  Hypothesis.2  —  Among  the  atmos- 
pheric hypotheses,  the  one  which  Chamberlin  has  put  into  its 
best  form  "is  based  chiefly  on  a  postulated  variation  in  the  con- 
stituents of  the  atmosphere,  especially  in  the  amount  of  carbon 
dioxide  and  water.  Both  these  elements  have  high  capacities  for 
absorbing  heat,  and  both  are  being  constantly  supplied  and  con- 
stantly consumed.  .  .  .  The  great  elevation  of  the  land  at  the  close 
of  the  Tertiary  seems  to  afford  conditions  favorable  both  for  the 
consumption  of  carbon  dioxide  in  large  quantities,3  and  for  the 
reduction  of  the  water  content  of  the  air.  Depletion  of  these  heat- 
absorbing  elements  was  equivalent  to  the  thinning  of  the  thermal 
blanket  which  they  constitute.  If  it  was  thinned,  the  temperature 
was  reduced,  and  this  would  further  decrease  the  amount  of  water 
vapor  held  in  the  air.  The  effect  would  thus  be  cumulative.  The 
elevation  and  extension  of  the  land  would  also  produce  its  own 
effects  on  the  prevailing  winds  and  in  other  ways,  so  that  some  of 
the  features  of  the  Hypsometric  (elevation)  hypothesis  form  a 
part  of  this  hypothesis.  .  .  .  By  variations  in  the  consumption  of 
carbon  dioxide,  especially  in  its  absorption  and  escape  from  the 
ocean,  the  hypothesis  attempts  to  explain  the  periodicity 4  of 

1  It  should  of  course  be  remembered  that  the  proper  temperature  con- 
ditions for  glaciation  may  have  recurred  many  times  when  other  factors 
such  as  requisite  precipitation  of  snow  may  not  have  obtained,  and  hence 
great  ice  sheets  may  not  actually  have  formed. 

2  For  a  fuller  treatment  of  this  hypothesis  see  Chamberlin  and  Salisbury's 
Geology,  Vol.  3,  pp.  432-446. 

3  Much  carbon  dioxide  is  used  up  in  the  decomposition  or  carbonation  of 
the  rocks.        4  That  is,  the  successive  advances  and  retreats  of  the  ice  sheets. 


364  HISTORICAL  GEOLOGY 

glaciation.  Localization  (of  glaciation)  is  attributed  to  the  two 
great  areas  of  permanent  low  pressure  in  proximity  to  which  the 
ice  sheets  developed."  1 

In  conclusion  we  may  say  that,  as  is  true  of  so  many  other 
great  natural  phenomena,  no  one  hypothesis  or  explanation  is 
sufficient  to  account  for  all  the  features  of  glacial  epochs.  Probably 
several  or  all,  or  at  least  parts  of  several  or  all,  of  the  above  hypoth- 
eses must  be  properly  combined  in  order  to  explain  the  phenomena 
of  glaciation,  and  hence  it  is  more  readily  understood  why  great 
glacial  epochs  have  not  been  more  common  throughout  the  history 
of  the  earth. 

POST-GLACIAL  (RECENT)  HISTORY  OF  THE  GLACIATED  AREA 

We  have  already  shown  that,  about  the  beginning  of  the  Glacial 
epoch,  the  north  Atlantic  Coast  region  at  least  w,as  much  higher 
than  it  is  today,  positive  proof  for  this  being  afforded  by  the 
submerged  lower  Hudson,  St.  Lawrence,  and  other  channels 
which  must  have  been  cut  when  the  land  was  higher.  Toward 
the  close  of  the  Glacial  epoch,  and  shortly  after,  we  know  that 
the  land  was  relatively  lower  even  than  it  is  today.  It  was 
during  this  time  of  subsidence  (sometimes  called  the  Champlain 
epoch)  that  the  lower  Hudson  and  St.  Lawrence  channels  were 
submerged  and  the  sea  coast  was  transferred  to  more  nearly  its 
present  position.  But  the  land  being  even  lower  than  now,  the 
lowlands  of  Long  Island  and  in  the  vicinity  of  New  York  City 
were  under  water  and  a  narrow  arm  of  the  sea  extended  through 
the  Hudson  and  Champlain  Valleys  to  join  a  broad  arm  of  the 
sea  which  reached  up  the  St.  Lawrence  Valley  and  possibly  even 
into  the  Ontario  Basin  (see  Fig.  220).  This  so-called  Champlain 
Sea  existed  at  the  time  of  the  Nipissing  stage  of  the  Great  Lakes 
already  described.  Champlain  Sea  beaches,  containing  marine 
shells  and  the  bones  of  Walruses  and  Whales,  have  been  found 
at  altitudes  of  about  400  feet  near  the  southern  end  of  Lake 
Champlain,  500  feet  at  its  northern  end,  and  600  or  more  feet 
at  the  eastern  end  of  Lake  Ontario.  In  the  lower  Hudson  Valley 
the  deposits  of  this  age  are  about  70  feet  above  sea  level,  and 
at  Albany  a  little  over  300  feet.  The  altitudes  of  these  so-called 
raised  beaches  show  how  much  lower  the  land  was  during  the  time 
*  Chamberlin  and  Salisbury:  College  Geology,  pp.  898-899. 


THE  QUATERNARY  PERIOD  365 

of  greatest  submergence,  and  that  the  subsidence  was  most  toward 
the  north.  That  this  greatest  submergence  occurred  after  the 
close  of  the  Ice  age  in  this  region,  is  proved  by  the  fact  that  the 
now  raised  beaches  and  marine  deposits  rest  upon  the  last  or  Wis- 
consin ice  drift. 

The  most  recent  movement  of  the  earth's  crust  in  the  region 
under  discussion  was  the  very  gradual  elevation  which  expelled 
the  Champlain  Sea  and  left  the  land  at  its  present  altitude.  The 
altitudes  of  the  raised  Champlain  beaches  show  that  the  greatest 
elevation  was  on  the  north.  The  warping  of  the  Iroquois  Lake 
beaches  already  described  occurred  at  this  same  time.  Actual 
surveys  during  the  past  century  have  proved  that  this  upward 
movement  in  the  northern  Great  Lakes  region  is  still  progressing 
at  the  rate  of  5  inches  in  100  miles  in  100  years. 

QUATERNARY  CONDITIONS  IN  THE  NON-GLACIATED  REGIONS 

Over  many  parts  of  the  continent  there  was  deposition  of  sed- 
iments during  Quaternary  time  outside  of  the  glaciated  area,  but 
little  or  nothing  can  be  done  by  way  of  correlating  these  with 
different  glacial  and  interglacial  stages  because  of  the  lack  of  the 
usual  means  of  comparison.  These  deposits  were  of  various  sorts, 
including  those  of  river  flood-plain,  wind,  terrestrial,  lacustrine, 
volcanic,  and  marine  origin. 

Atlantic  and  Gulf  Coasts.  —  On  the  Atlantic  and  Gulf  Coastal 
Plains,  and  in  addition  to  the  Lafayette  (Pliocene?)  already  de- 
scribed, there  is  a  well-known  series  of  unconsolidated  deposits  of 
sands,  gravels,  clays,  etc.,  usually  comprised  under  the  name 
Columbia.  Like  the  Lafayette,  the  Columbia  is  wholly  a  surficial 
deposit  but  at  lower  altitudes,  never  rising  more  than  a  few  hun- 
dred feet  above  sea  level  and  generally  less  than  200  feet.  On  the 
north  Atlantic  Coastal  Plain,  at  least,  the  Columbia  is  pretty 
clearly  divisible  into  three  formations  (Sunderland,  Wicomico, 
and  Talbot),  each  of  which  is  represented  topographically  by  a 
more  or  less  distinct  terrace  with  the  oldest  at  the  top. 

There  has  been  much  difference  of  opinion  regarding  the  origin 
and  significance  of  these  Columbia  deposits,  but  they  are  now  quite 
certainly  known  to  be  marine  terraces.  According  to  Shattuck,1 
each  of  the  formations  and  terraces  of  the  Columbia  is  explained 

1  G.  B.  Shattuck:   Pliocene  and  Pleistocene,  Md.  Geol.  Survey,  p.  137. 


366  HISTORICAL  GEOLOGY 

as  due  to  subsidence  (or  submergence)  below  sea  level  and 
deposition  of  sediments,  followed  by  elevation  (or  emergence) 
and  erosion.  The  fossil  evidence  regarding  non-marine  or  marine 
origin  of  the  deposits  is  far  from  conclusive. 

Western  United  States.  —  Quaternary  deposits,  representing 
many  types  of  origin,  are  known  in  the  west. 

Volcanic  deposits  of  this  age  in  the  west  are  not  always  clearly 
separable  from  those  of  the  Tertiary,  but  it  is  certain  that  pretty 
vigorous  vulcanism  continued  into  the  Quaternary.  Such  volcanic 
deposits,  including  lava-flows,  cinders,  and  volcanic  ashes,  are 
known  in  New  Mexico,  Utah,  Idaho,  and  all  the  states  farther 
west  as  well  as  in  Alaska.  Mount  Shasta  shows  lava  flows  of  post- 
Glacial  or  recent  age,  while  small  lava  fields  and  cinder  cones  in 
northern  and  southern  California  and  in  northern  Arizona  must  be 
of  late  Quaternary  age  because  they  are  so  unaffected  by  weather- 
ing and  erosion.  As  already  mentioned  in  the  discussion  of 
Tertiary  vulcanism,  a  cinder  cone  and  small  lava  field  have  cer- 
tainly been  built  up  within  the  last  200  years,  while  Lassen  Peak 
in  northern  California  is  now  (1916)  actually  in  eruption. 

At  the  bases  of  mountains  throughout  the  arid  and  semi-arid 
regions  of  the  west,  great  accumulations  of  talus  and  alluvial 
materials  took  place.  Some  of  the  alluvial  cones  or  fans  have  a 
thickness  of  fully  a  thousand  feet.  Extensive  flood-plain  deposits 
are  found  in  many  places. 

Recent  studies  have  shown  that  the  wind  has  been,  and  is,  a 
very  important  agent  of  erosion  and  deposition,  particularly  in 
the  arid  western  regions.  Deep  and  extensive  wind-blown  deposits 
are  still  forming  in  many  of  the  intermontane  basins. 

During  part  of  the  Quaternary,  at  least,  the  Great  Basin  region 
had  a  moister  climate  than  at  present,  because  lakes  were  much 
more  numerous  and  larger  than  now  (Fig.  227) .  One  of  the  largest 
of  these  was  Lake  Bonneville,  which  represented  a  greatly  enlarged 
stage  of  the  Great  Salt  Lake.  Lake  Bonneville  was  of  fresh  water; 
covered  19,000  square  miles;  and  had  a  maximum  depth  of  1000 
feet.  Its  remnant,  the  present  heavy  brine  of  the  Great  Salt  Lake, 
covers  about  2000  square  miles  and  has  a  maximum  depth  of 
only  about  50  feet.  The  outlet  of  Lake  Bonneville  was  northward 
into  Snake  River.  The  former  existence  of  this  great  body  of  water 
is  positively  proved  by  the  perfectly  preserved  beaches,  wave-cut 
terraces,  deltas,  etc.  Another  very  large  body  of  water,  called 


THE  QUATERNARY  PERIOD 


367 


Lake  Lahontan,  occupied  some  thousands  of  square  miles  of  west- 
ern Nevada,  but  it  had  no  outlet.  Since  the  lowering  of  the  water 
levels  in  these  basins,  crustal  disturbances  have  caused  a  tilting  of 
the  old  shore  lines  some  hundreds  of  feet. 

Locally,  along  the  Pacific  border,  Quaternary  fossiliferous 
marine  deposits  occur  up  to  altitudes  of  200  or  300  feet  or  more. 
"  Important  and  more  or  less  widespread  periods  of  diastrophism 
later  than  the  one  terminating  the  Monterey  (middle  Miocene) 
period  of  deposition 
occurred  in  the  Pleis- 
tocene. .  .  .  Minor 
movements  produc- 
ing local  unconform- 
ities took  place  in 
central  and  southern 
California  at  various 
times  during  the 
Pleistocene  in  addi- 
tion to  the  more 
far-reaching  disturb- 
ances in  the  same 
epoch."  1 

The    islands    off 


Fig.  227 

Map  showing  extent  of  the  extinct  Lakes  Bonne- 
ville  (a)  and  Lahontan  (6)  in  the  western  United 
States.  Heavy  black  lines  are  axes  of  Sierra 
Nevada  and  Wasatch  Mountains  respectively, 
c,  area  of  Great  Salt  Lake.  (After  Gilbert  and 
Russell,  from  Le  Conte's  "Geology,"  permission 
of  D.  Appleton  and  Company.) 


the  coast  of  southern 
California  were  con- 
nected  with  the 
mainland  late  in  the 
Tertiary,  or  early  in 
the  Quaternary,  as  shown  by  the  flora,  and  in  one  case  the  remains 
of  a  Mammoth.  A  subsidence,  causing  the  separation  of  the  islands 
from  the  mainland,  was  followed  by  partial  re-elevation  to  the  ex- 
tent of  at  least  1500  feet,  as  proved  by  the  raised  sea-beaches  on 
the  mainland  and  on  some  of  the  islands.  A  remarkable  fact  is 
that  some  of  the  adjacent  islands  were  subsiding  during  this  whole 
time.  Raised  beaches  near  San  Francisco  testify  to  Quaternary 
upward  movements  of  1500  to  1800  feet.  Similar  beaches  on  the 
northern  coast  of  Oregon  lie  at  200  feet  or  more  above  the  sea. 


Ralph  Arnold:   Outlines  of  Geologic  History,  by  Willis  and  Salisbury. 


368 


HISTORICAL  GEOLOGY 


THE  GLACIAL  EPOCH  IN  EUROPE 

In  many  important  respects  the  history  of  the  Quaternary 
period  in  Europe  is  much  like  that  of  North  America.  The  accom- 
panying map  (Fig.  228)  shows  the  extent  (about  600,000  square 
miles)  of  the  ice  sheet  at  the  time  of  maximum  glaciation.  As  the 
map  also  shows,  the  great  center  of  dispersal  was  over  the  Scandi- 
navian peninsula,  with  apparently  a  small,  secondary  centre  over 
Scotland.  The  ice  over  Scandinavia  is  estimated  to  have  been 

6000  to  7000  feet 
deep.  The  Baltic, 
North,  and  Irish 
Seas  were  completely 
filled  by  the  great  ice 
sheet  which  extended 
well  south  into  Ger- 
many and  Russia.  As 
in  North  America, 
five  or  six  glacial  and 
interglacial  stages 
have  been  recognized. 


Fig.  228 

Map  showing  the  extent  of  ice  in  Europe  at  the 
time  of  maximum  glaciation.  (After  J.  Geikie, 
from  Norton's  "Elements  of  Geology,"  by  per- 
mission of  Ginn  and  Company,  Publishers.) 


During  the  Glacial 
epoch,  the  glaciers  of 
the  Alps  were  far 
larger  and  more 
numerous  than  today,  and  they  often  flowed  down  to  the  lowlands 
on  all  sides.  The  Pyrenees  and  the  Caucasus  Mountains  were 
also  vigorously  glaciated. 

As  in  North  America,  also,  northern  Europe  was  notably  higher 
than  now,  apparently  late  in  the.  Tertiary  or  early  in  the  Quater- 
nary; then,  toward  the  close  of  the  Glacial  epoch,  there  was  sub- 
sidence (of  Scandinavia  at  least)  to  below  the  present  level;  and 
this  was  followed  by  partial  re-elevation  of  at  least  some  hundreds 
of  feet  to  the  present  level.  Actual  surveys  have  proved  that  from 
central  to  northern  Sweden  the  land  is  still  rising.  The  great 
fiords  of  Norway,  with  their  raised  beaches,  testify  to  the  impor- 
tant changes  of  level  above  mentioned. 

In  other  continents  many  of  the  higher  mountains  bore  glaciers, 
even  where  none  at  all  exist  today.  Also,  so  far  as  known,  the 
Antarctic  region  was  heavily  glaciated  much  as  it  is  today. 


THE  QUATERNARY  PERIOD 


369 


LIFE  OF  THE  QUATERNARY 

The  species  of  plants  and  invertebrate  animals  of  the  whole 
Quaternary  period  were  much  the  same  as  those  now  living;  there- 
fore we  shall  pass  them  by  without  special  description.  Among 
the  Vertebrate  animals,  the  species  of  the  lower  classes,  such  as 
Fishes,  Amphibians,  Reptiles,  and  Birds,  were  almost  all  the  same 


Fig.  229 

A  great  Ground-sloth,  Megatherium  americanum.     (After  W.  B.  Scott,  by 
permission  of  The  Macmillan  Company.) 

as  those  now  living,  but  in  the  highest  class  of  Vertebrates  (Mam- 
mals) there  were  important  changes. 

Mammals,  except  Man.  —  One  of  the  most  characteristic 
features  of  Quaternary  (especially  Pleistocene)  Mammals  was  the 
great  size  of  so  many.  In  fact,  as  regards  size  and  diversity  of 
forms,  the  Mammals  may  be  said  to  have  attained  their  culmina- 
tion during  the  Pleistocene  epoch.  Comparing  the  Mammals  of 
that  epoch  with  those  of  today,  we  find  that  many  species,  espe- 


370 


HISTORICAL  GEOLOGY 


cially  of  the  large  animals,  have  become  extinct,  and  the  world 
is  now  (except  for  Man)  said  to  be  " zoologically  impoverished." 
The  vicissitudes  of  the  climate,  i.e.  alternations  of  glacial  and 
interglacial  conditions,  appear  to  have  "  produced  a  very  severe 
struggle  for  existence  and  were  fatal  to  a  great  many  large  Mam- 
mals, causing  numerous  extinctions  over  the  larger  part  of  the 


Fig.  230 

Great  armored  Glyptodonts,  Doedicurus  clavicaudatus  and  Glyptodon  davipes. 
(After  W.  B.  Scott,  by  permission  of  The  Macmillan  Company.) 

world"  (W.  B.  Scott).  It  is  our  present  purpose  to  refer  to  only 
a  few  of  the  most  interesting  now  extinct  Pleistocene  Mammals. 
Among  the  Edentates  (Sloths,  Armadillos,  etc.),  which  belong  to 
the  simplest  Placental  Mammals,  the  Megatherium  and  the 
Glyptodon  are  of  special  interest.  The  former  (see  Fig.  229),  a  sort 
of  giant  ground  Sloth,  was  remarkably  massive  and  attained  a 
length  of  15  to  18  feet.  Its  thigh  bones  were  two  or  three  times 
the  thickness  of  those  of  the  Elephant,  and  its  front  feet  were  about 
a  yard  long.  The  tooth  structure  shows  it  to  have  been  a  plant 


THE   QUATERNARY  PERIOD  371 

feeder.  This  powerful  creature  could  easily  have  toppled  over 
small  trees  in  order  to  strip  off  the  leaves.  The  Glyptodon  (see 
Fig.  230)  was  a  giant  Armadillo  up  to  8  feet  long  and  armed  with 
a  very  strong  turtle-like  carapace.  These  Edentates,  including 
many  species,  were  common  in  South  America  and  in  North  Amer- 
ica as  far  north  as  Pennsylvania  and  Oregon. 

The  Proboscidians  were  well  represented  by  both  the  Mastodons 
and  the  Mammoths.  These  were  smaller  than  those  of  the  late 
Tertiary  or  about  the  size  of  modern  Elephants.  "During  Pleisto- 
cene times  the  Proboscidia  covered  all  of  the  great  land  masses 
except  Australia,  but  were  diminishing  in  numbers,  and  toward 
the  close  of  the  Pleistocene  the  period  of  decadence  began,  result- 
ing in  the  extinction  of  all  but  the  Indian  and  African  Elephants 
of  today."  l  The  Mastodon  roamed  only  over  much  of  North 
America  and  part  of  South  America,  having  become  extinct  in  the 
Old  World  in  the  late  Tertiary.  The  Mammoth  had  a  much  wider 
range  from  the  Atlantic  states  to  Alaska;  across  Siberia;  through 
central  Europe;  and  even  to  the  British  Isles.  Fine  examples  of 
the  almost  perfect  preservation  of  entire  organisms  of  now  extinct 
forms  are  furnished  by  specimens  of  frozen  Mammoths  which 
have  been  in  nature's  "cold  storage"  for  thousands  of  years  in  the 
gravels  or  ice  of  Siberia.  In  several  cases  much  of  the  hide,  long 
brown  hair,  and  even  the  flesh  are  known  to  have  been  perfectly  pre- 
served, the  flesh  having  been  eaten  by  dogs  or  even  the  natives 
themselves.  Two  of  the  finest  specimens  were  discovered  in  1806 
and  1901. 

In  addition  to  the  above-mentioned  animals  in  North  America, 
were  gigantic  Bisons,  with  spread  of  horns  up  to  10  feet;  great 
Moose-like  Elks;  Rodents,  up  to  5  feet  long;  Sabre-toothed  Tigers; 
huge  Lions,  and  several  species  of  Zebra-like  Horses. 

Distribution  of  Quarternary  Plants  and  Animals.  —  The 
alternations  of  glacial  and  interglacial  climates  caused  corres- 
ponding migrations  of  colder  and  warmer  climate  animals  and. 
plants.  While  a  great  ice  sheet  was  advancing,  Arctic  animals 
and  plants  ranged  farther  and  farther  southward  even  into  what 
are  now  temperate  latitudes.  Thus  the  Musk-ox  ranged  southward 
to  Iowa  and  Kentucky,  and  the  Walrus  to  Virginia,  while  in  Europe 
the  Reindeer,  Arctic  Fox,  etc.,  ranged  southward  into  France. 
During  the  retreat  of  a  great  ice  sheet,  the  Arctic  fauna  and  flora 
1  R.  S,  Lull:  Amer.  Jour.  Sci.,  Vol.  25,  March,  1908,  p.  11. 


372  HISTORICAL  GEOLOGY 

retreated  to  colder  climatic  conditions,  either  by  following  the  ice 
front  northward  or  by  going  up  the  mountains  as  they  were  freed 
from  the  ice.  This  retreat  up  the  mountains  affords  a  ready 
explanation  of  the  fact  that  certain  Arctic  plants  and  animals 
(especially  Insects)  are  now  found,  in  the  Alps  and  higher  parts 
of  the  White  Mountains  of  New  Hampshire,  separated  from  their 
former  habitat  by  many  hundreds  of  miles  of  climate  now  too 
mild  for  them  to  cross. 

Until  late  in  the  Quaternary,  the  geographical  environment 
favored  a  very  widespread  distribution  of  Mammals  over  most  of 
the  land  areas.  Thus  North  America  and  South  America  were 
connected;  North  America  and  Asia  were  joined  across  what  is 
now  the  Bering  Sea;  and  Eurasia  and  Africa  were  well  connected. 
Australia  was  one  of  the  largest  isolated  land  masses,  and  herein 
lies  the  explanation  of  its  most  peculiar  fauna  and  flora.  For 
example,  of  the  many  known  species  of  Mammals  all  are  non- 
Placentals,  that  is  they  are  Monotremes  and  Marsupials.  Non- 
Placentals  inhabited  most  of  the  great  land  areas  (including 
Australia)  during  the  Mesozoic  era.  Since  true  Placental  Mam- 
mals made  their  appearance  in  the  early  Tertiary,  it  is  quite 
certain  that  Australia  was  isolated  from  the  Asiatic  continent 
before  the  Tertiary  and  that  under  the  more  local  conditions 
and  less  severe  struggle,  Placentals  were  never  evolved  there 
and  they  never  could  get  there  from  other  continents,  except 
as  artificially  introduced  by  Man. 

Madagascar  also  has  a  mammalian  fauna  very  peculiar  to  itself. 
This  island  was  separated  from  the  mainland  before  Quaternary 
time,  and  its  Mammals,  because  of  less  severe  struggle  for  existence, 
have  changed  more  slowly  and  in  their  own  way  as  compared  with 
those  of  the  African  continent. 

The  coast  islands  of  southern  California  show  similar  rela- 
tion to  the  mainland,  but  more  especially  as  regards  the  plant 
species. 

Antiquity  of  Man.  —  Thus  far  we  have  said  little  about  the 
interesting  and  important  subject  of  Man's  first  appearance,  and 
nothing  about  his  early  history.  Since  Man,  who  represents  the 
very  highest  type  of  organism  which  has  ever  inhabited  the  earth, 
belongs  to  one  of  the  most  recent  and  important  groups  of  animals, 
it  is  appropriate  that  a  brief  discussion  of  his  origin  and  early 
history  be  reserved  for  the  very  last.  Up  to  the  present,  at  least, 


THE  QUATERNARY  PERIOD  373 

progressive  organic  evolution  through  the  many  millions  of  years 
has  reached  its  climax  in  Man. 

Because  of  additional  discoveries  and  better  methods  of  study, 
our  knowledge  of  prehistoric  Man  is  becoming  more  satisfactory 
year  by  year.  The  ablest  students  of  the  subject  are  agreed  upon 
several  important  points,  while  regarding  others  there  is  still  much 
disagreement.  There  is  quite  a  general  agreement  (1)  that  Man 
(physical  Man  at  least)  has  evolved  from  lower  forms  of  Primates; l 
(2)  that  there  are  clearly  recognizable  at  least  two  types  or  species 
of  Man,  namely,  (a)  Homo  primigenius  (Paleolithic),  a  primitive 
type  now  extinct,  and  (b)  Homo  sapiens  (Neolithic,  to  modern), 
represented  by  existing  Man ;  (3)  that  true  Man  certainly  existed 
during  the  Pleistocene;  (4)  that,  on  a  most  conservative  basis,  true 
Man  was  on  the  earth  no  less  than  100,000  years_ago;  and  (5)  that 
there  is  no  positive  evidence  for  the  existence  of  true  Man  earlier 
than  the  Pleistocene  or  Glacial  epoch. 

Differences  of  opinion  commonly  surround  such  as:  (1)  The 
classification  of  the  early  ancestral  forms,  that  is  whether  they 
should  be  called  Apes,  Man-like  Apes,  or  Ape-like  Men; 2  and  (2) 
the  portions  of  the  Quaternary  system  represented  by  the  deposits 
in  which  Man's  bones  or  implements  are  found,  or  by  the  remains 
of  animals  found  associated  with  Man's  bones  or  implements. 

Bones  and  implements  of  ancient  Man  and  his  early  ancestral 
forms  are  found  chiefly  in  high  river  terraces,  loess,  caves,  and 
glacial  deposits.  In  this  connection,  it  should  be  stated  that,  in 
spite  of  various  reported  discoveries,  there  is  no  well  proved  evi- 
dence for  Man's  existence  in  North  America  during  the  Pleistocene. 

The  following  tabular  arrangements  are  introduced  in  order 
to  graphically  represent  (synoptically)  certain  of  the  most  signifi- 
cant features  in  connection  with  the  geologic  history  of  Man.  The 
first  table  is  by  Clark  Wissler  and  the  second  by  the  author.  It 
should  be  clearly  borne  in  mind  that,  in  some  respects,  these 
are  only  tentative  arrangements,  though  they  do  summarize  our 

1  There  is  a  prevalent  popular  misconception  that  the  evolutionist  con- 
siders Man  to  be  a  direct  descendant  of  the  Monkey.    What  the  evolutionist 
really  believes,  however,  is  that  Man  and  Monkey  may  have  sprung  from  a 
common  ancestry. 

2  It  is  important  to  note  that  this  very  difference  of  opinion  is  one  of  the 
strongest  arguments  in  favor  of  the  organic  evolution  of  Man,  because  prac- 
tically all  intermediate  types  between  true  Men  and  certain  higher  Primate 
forms  are  known. 


374 


HISTORICAL  GEOLOGY 


most  recent  knowledge  based  upon  the  work  of  able   students 

of  the  subject. 

The  introduc- 
tion  of  the  so- 
called  "Eolithic" 
period  into  this 
table  seems  doubt- 
fully appropriate 
in  the  light  of  our 
best  knowledge, 
though  it  is  possi- 
ble that  certain 
very  rude  stone 
implements  such 
as  those  found  by 
Prestwich  in  the 
high  river  gravels 
in  Kent  (Eng- 
land) belong 
to  such  an  early 
period. 


Fig.  231 

Table  to  show  the  principal  geologic  stages  in  the 
history  of  Man.  (After  C.  Wissler,  courtesy  of  the 
American  Museum  of  Natural  History.) 


3.  Homo  sapiens 

(e.g.  modern  Men). 


Historic  (bronze  and  iron)  age. 
Neolithic  (" recent  stone")  age. 

(Carefully    shaped    and    polished 

stone  implements.) 


Modern. 

Post-Glacial 
but  pre- 
Historic. 


2.  Homo  primigenius 

(Primitive  Men,  e.g. 
Men  of  Neanderthal, 
La  Chapelle,  Spy, 
Krapina,  etc.). 


Upper  Paleolithic  ("ancient  stone") 
age.  (Rough  bone  and  stone  im- 
plements, cave  frescoes,  bone  car- 
vings, etc.) 

Lower  Paleolithic  ("ancient  stone") 
age.  (Rude  stone  implements  of 
so-called  "River  Man.") 


Late    Pleisto- 
cene. 

Middle    Pleis- 
tocene. 


1.  Early  ancestral  forms 
(Apes,  or  Man-like 
Apes,  e.g.  Pithecan- 
thropus erectus  and 
Homo  heidelbergen- 


(No  known  implements.) 


Early  Pleisto- 
cene 
or 
Pliocene. 


THE  QUATERNARY  PERIOD 


375 


Early  Ancestral  Forms.  —  Among  the  most  ancient  known 

remains  of  Man's  early  ancestral  forms,  two  are  of  special  interest. 

These  are  the  so- 
called  Pithecan- 
thropus erectus  and 

Homo    heidelber- 

gensis     which     are 

of  greater  antiquity 

than  any  bones  of 

undoubted    human 

beings. 

Pithecanthropus 

erectus  was  found  in 

Java  in  1891  and, 

according  to  its  dis- 
coverer (Dubois), 

it  was  of  Pliocene 

age    and    had    an 

erect    attitude. 

Others,     however, 

who  have  examined 

the  locality  and  the 

remains    claim    its 

age  to  have  been  not  earlier  than  early  Pleistocene,  and  that  there 

is  no  proof  whatever  that 
it  had  an  erect  attitude. 
The  actual  remains  in- 
clude the  upper  portion 
of  a  skull,  *a  lower  Jaw, 
several  teeth,  and  aTleft 
thigh  bone.  A  consider- 
able amount  of  sediment 
rested  upon  the  remains. 

So-called  Homo  heidel- 
bergensis,  represented  by  a 
lower  jaw  with  a^number 
FiS-  233  of   teeth    well    preserved, 

Restoration  of  the  head  of  Pithecanthropus     wag  Discovered  (1907)  near 
erectus.     (After  Du  Bois,  from  Norton  s      H  «H  lh         Germanv  in  a 
"Elements  of  Geology,"  by  permission      Heidelberg,  Germany  11 
of  Ginn  and  Company,  Publishers.)  sand-pit   seventy  teet    be-. 


Fig.  232 

Comparison  of  skull  profiles  of  lowest  types  of  Men 
and  highest  Apes.  Papua,  modern  native  of  New 
Guinea;  Spy  1  and  2,  Men  of  Spy;  Nt,  Neander- 
thal Man;  Pe,  Pithecanthropus  erectus;  HI,  a 
Gibbon;  At,  a  modern  Chimpanzee.  (By  Marsh 
after  Du  Bois,  from  Le  Conte's  "Geology," 
courtesy  of  D.  Appleton  and  Company.) 


376  HISTORICAL  GEOLOGY 

low  the  surface.  In  this  case,  as  well  as  that  of  Pithecanthropus, 
the  depth  of  over-lying  materials  and  the  close  associations  of  the 
remains  of  other  Mammals,  including  certain  now  extinct  species 
(e.g.  Rhinoceros  etruscus),  pretty  clearly  point  to  an  age  not  later 
than  about  the  early  Pleistocene. 

Summarizing  the  characteristics  of  the  forms  represented  by 
these  two  specimens  (Pithecanthropus  erectus  and  Homo  heidel- 
bergensis),  Duckworth  says:  "Evidence  exists  in  each  case  to  the 
effect  that  far-distant  human  ancestors  are  hereby  revealed  to 
their  modern  representatives.  Of  their  physical  characters,  dis- 
tinct indications  are  given  of  the  possession  of  a  small  brain  in  a 
flattened  brain-case  (see  Fig.  234)  associated  with  powerful  jaws 


a  b  c 

Fig.  234 

Comparison  of  skulls:  a,  modern  Chimpanzee;  6,  Paleolithic  Man; 
c,  modern  Frenchman.  (After  E.  Rivet,  from  New  York  State 
Museum  Bulletin  173.) 

and  massive  continuous  brow-ridges;  the  lower  part  of  the  face 
being  distinguished  by  the  absence  of  any  projection  of  the  chin. 
The  teeth  indicate  with  some  degree  of  probability  that  their  diet 
was  of  a  mixed  nature,  resembling  in  this  respect  the  condition  of 
many  modern  savage  tribes.  .  .  .  Whether  they  habitually  as- 
sumed the  distinctive  erect  attitude  is  a  point  still  in  doubt.  .  .  . 
It  is  probable  that  in  stature  they  were  comparable,  if  not  superior 
to,  the  average  man  of  today. " l  It  seems  clear,  therefore,  that 
these  remains  represent  a  type  intermediate  between  Men  and  the 
more  highly  developed  Apes.  »  /V 

Paleolithic  Men.  —  Many  examples  of  the  bones  and  imple- 
ments of  Pleistocene  Men  have  been  found  in  Europe,  principally 
in  caves  within  and  without  the  glaciated  area.  It  is  very  difficult, 
if  not  impossible,  in  any  case  to  determine  the  precise  glacial  or 

1  W.  H.  L.  Duckworth:  Prehistoric  Man,  pp.  60-61. 


THE  QUATERNARY  PERIOD  377 

interglacial  stage  to  which  such  specimens  belong,  but  their 
"  great  antiquity  is  inferred  from  the  circumstances  under  which 
they  were  discovered.  The  evidence  relates  either  to  their  associa- 
tion with  extinct  animals  such  as  the  Mammoth,1  or  again  the 
bones  may  have  been  found  at  considerable  depths  from  the  sur- 
face, in  strata  judged  to  have  been  undisturbed  since  the  remains 
were  deposited"  (W.  H.  L.  Duckworth).  These  Pleistocene  Men 
are  called  Paleolithic  because  they  are  known  to  have  fashioned 
manynide  stone  implements  or  weapons.  Although  their  struc- 
ture, par ticuterTy"  ofthe Tskull,  shows  them  to  have  been  low  type 
savages,  nevertheless  all  agree  that  they  were  truly  human  though 
of  different  species  from  modern  Men.  It  is  generally  customary 
to  group  the  more  typical  examples  of  Paleolithic  Men  together 
under  the  name  Homo  primigenius,  while  modern  Men  are  called 
Homo  sapiens.  The  nearest  living  approaches  to  the  Paleolithic 
type  are  such  as  the  native  Papuan  of  New  Guinea  or  the  Bush- 
man of  Australia.  That  Paleolithic  Men  hunted  the  wild  beasts 
of  their  day  is  certain  because  of  the  direct  and  frequent  associa- 
tions of  the  bones  of  such  animals  with  their  own. 

A  few  of  the  best  known  and  more  typical  examples  of  Paleo- 
lithic Men  will  now  be  described.  "In  a  cave  at  Neanplertti.aJ^ 
near  Diisseldorf,  was  found  (1856)  a  very  remarkable  human 
skeleton,  which  has  greatly  excited  the  interest  of  the  scientific  men. 
The7'  limb-bones  are  large,  and  the  protuberances  for  muscular 
attachments  very  prominent;  ^the  skull  very  thick,  very  low  in  the 
arch,  and  very  prominent  in  the  brows.  It  has  been  supposed  by 
some  to  be  an  intermediate  form  between  Man  and  the  Ape;  but, 
according  to  the  best  authority,  it  is  in  no  respect  intermediate, 
but  truly  human.  It  is  probably  the  skeleton  of  a  man  exception- 
ally muscular  in  body  and  low  in  intelligence  (see  Fig.  232).  ... 
Recently  there  have  been  found  in  a  cave  at  Spy,  Belgium,  two 
nearly  complete  skeletons,  which  seem  to  be  of  the  same  type  as 
the  Neanderthal  Man,  and  with  the  latter  are  supposed  to  belong 
to  a  distinct  and  very  early  race.  They  are  believed  to  have  been 
Men  of  short  stature,  broad  shoulders,  bowed  thighs,  slightly  bent 
knees,  and  semi-erect  posture,  but  nevertheless  distinctly  human. 
The  skeletons  were  found  associated  with  the  remains  of  all  the 

1  Also  Cave-Bear,  Cave-Hyena,  woolly  Rhinoceros,  Reindeer,  Musk- 
Ox,  Hippopotamus,  etc.,  which  are  either  wholly  extinct  or  extinct  in 
Europe. 


378  HISTORICAL  GEOLOGY 

characteristic  Quaternary  animals  and  with  implements  of  the 
rudest  kind. " l 

In  the  Perigord  district  of  southwestern  France  there  are  a 
number  of  caves  in  which  were  found  relics  of  Men  which  are 
thought  to  range  from  early  to  late  Paleolithic  time.  Among  the 
more  interesting  relics  are  fish-hooks  made  of  bone,  and  crude 
drawings  of  certain  animals  with  which  the  Men  were  familiar, 
such  as  the  Mammoth,  which  is  now  wholly  extinct,  and  the  Rein- 
deer and  Horse,  now  (naturally)  extinct  in  that  region. 

The  Aurignac  cave  of  France  was  probably  a  family  or  tribal 
burial  place.  Near  the  entrance  were  found  ashes  and  cinders 
mixed  with  split  and  burnt  bones  of  now  extinct  animals.  Within 
the  cave  were  seventeen  human  skeletons  of  various  sizes  associated 
with  ancient  art  works  and  bones  of  extinct  animals. 

An  important  discovery  (1908)  was  in  a  cave  at  La  Chapelle- 
aux-Saints  (Correze) .  The  remains  are  a  nearly  perfectly  preserved 
skull  as  well  as  the  lower  jaw  and  many  bones  of  the  body.  In 
most  respects  the  specimen  very  closely  resembles  the  Neanderthal 
skeleton  above  described.  Among  animal  remains  found  associated 
with  this  skeleton  were  the  Reindeer,  Horse,  Bison?,  Rhinoceros, 
Ibex,  Wolf,  Marmot,  Badger,  and  Boar.  This  La  Chapelle  speci- 
men seems  to  be  a  very  fine  typical  example  of  the  Paleolithic,  or 
Neanderthal,  type  of  Man. 

Very  recently  (1911-1912)  an  important  discovery  was  made  at 
EiLtdown  Common  in  Sussex,  England.  The  remains  consist  of 
most  of  a  skull  and  lower  jaw,  with  portions  of  the  front  of  each 
missing.  After  considering  all  the  evidence,  Dawson  and  Wood- 
ward 2  say:  "It  appears  probable  that  the  skull  and  mandible 
cannot  safely  be  described  as  being  of  earlier  date  than  the  first 
half  of  the  Pleistocene  epoch,"  and  according  to  Woodward  the 
skull  represents  the  "  oldestJaqaically  human  brain-case  hitherto 
found."  The  lower  jaw  is  pretty  Ape-HkeTn  character,  while  the 
skull,  on  one  hand,  has  a  much  smaller  brain  capacity  than  the 
typical  examples  of  Paleolithic  Man  above  described,  and,  on 
the  other  hand,  the  front  (forehead)  of  the  skull  is  distinctly 
steeper  (relatively  higher)  than  in  typical  Paleolithic  Man,  this 
latter  feature  being  exceptionally  modern.  Because  of  this  un- 
usual combination  of  characters,  the  Piltdown  specimen  may 

1  J.  Le  Conte:  Elements  of  Geology,  5th  ed.,  p.  635. 

2  Dawson  and  Woodward:  Quar.  Jour.  Geol.  Soc.,  Mar.,  1913,  p.  123. 


THE  QUATERNARY  PERIOD 


379 


represent  a  different  species  and  has  been  named   Eanthropus 
dawsoni. 

Another  interesting  feature  concerning  Paleolithic  Man  is  the 
fact  that  many  caves  which  he  occupied  have  their  walls  decorated 
with  drawings  and  even  pictures  in  colors  —  veritable  art  galleries. 
One  of  the  finest  examples  is  the  Altamira  cavern  in  northern 


r 


Fig.  235 

A  charging  wild  Boar,  one  of  the  best  paintings  by  Paleolithic  Man  in  the 
cave  at  Altimira,  Spain.  (After  Cartailhac  and  Breuil,  courtesy  of  the 
American  Museum  of  Natural  History.) 

Spain.  "  As  we  gaze  at  the  pictures  one  of  the  first  things  to  impress 
us  is  the  excellence  of  the  drawing,  the  proportions  and  postures 
being  unusually  good.  The  grand  Bison  and  the  charging  Boar 
are  masterpieces  in  this  respect  (Fig.  235).  The  next  observation 
may  be  that,  in  spite  of  this  perfection  of  technique,  there  is  no 
perspective  composition  —  that  is,  no  attempt  to  combine  or  group 
the  figures  (Figs.  236,  237).  ...  In  addition  to  these  remarkable 
sketches  in  colors,  the  other  walls  of  Altamira  have  numerous 
figures  in  black  outline  and  also  engravings.  ...  It  is  also  clear 


380 


HISTORICAL  GEOLOGY 


Fig.  236 

The  "Procession  of  Mammoths";  a  painting  by  Paleolithic 
Man  in  a  cave  at  Font-de-Gaume  in  west-central  France. 
Note  the  lack  of  perspective  composition.  (After  Capitan 
and  Breuil,  courtesy  of  the  American  Museum  of  -Natural 
History.) 

that  the  work  of  many  different  artists  is  represented,  covering  a 
considerable  period  of  time.  The  walls  show  traces  of  many  other 
paintings  that  were  erased  to  make  way  for  new  work."  x 

Many  other  caves 
containing  works 
of  art  have  been 

»  discovered  in  north- 

XV  — \/  i      ern  Spain  and  in 

France. 

The  appearance 
of  true  Man  "was 
an  event  which  in 
importance  ranks 
with  the  advent  of 
life  upon  the  planet, 
and  marks  a  new 
manifestation  of  cre- 
ative energy  upon  a 
higher  plane.  There 
now  appeared  intelli- 
gence,  reason,  a 
moral  nature,  and  a 
capacity  for  self-di- 
rected progress  such  as  had  never  been  before  on  earth"  (W.  H. 
Norton). 

1  Clark  Wissler:  Amer.  Mus.  Jour.,  Dec.,  1912,  pp.  290-292. 


Fig.  237 

Line  cut  copy  of  a  Paleolithic  painting  in  the  cave 
at  Cogul,  Spain.  This  is  perhaps  the  only  known 
attempt  to  portray  human  beings.  (After  Car- 
tailhac  and  Breuil,  courtesy  of  the  American 
Museum  of  Natural  History.) 


THE  QUATERNARY  PERIOD  381 

itihfe  Man.  —  So  far  as  known  the  late  Paleolithic  passed 
gradually  into  the  Neolithic  or  recent  stone  age  when  Men  were 
more  highly  developed  and  similar  in  structure,  at  least,  to  those 
of  today.  The  stone  implements  of  Neolithic  Men  were  usually 
more  perfectly  made  and  often  polished.  "The  remains  of  Neo- 
lithic Man  are  found,  much  as  are  those  of  the  North  American 
Indians,  upon  or  near  the  surface,  in  burial  mounds,  in  shell  heaps 
(the  refuse  heaps  of  their  settlements),  in  peat-bogs,  caves,  recent 
flood-plain  deposits,  and  in  the  beds  of  lakes  near  shore  where  they 
sometimes  built  their  dwellings  upon  piles.  .  .  .  Neolithic  Man  in 
Europe  had  learned  to  make  pottery,  to  spin  and  weave  linen,  to 
hew  timber,  and  build  boats,  and  to  grow  wheat  and  barley.  The 
Dog,  Horse,  Ox,  Sheep,  Goat,  and  Hog  had  been  domesticated."  1 
This  stage  of  culture  gradually  passed  into  the  historic  age. 

"Man  is  linked  to  the  past  through  the  system  of  life,  of  which 
he  is  the  last,  the  completing  creation.  But,  unlike  other  species 
of  that  closing  system  of  the  past,  he,  through  his  spiritual  nature, 
is  more  intimately  connected  with  the  opening  future"  (J.  D. 
Dana). 

1  W.  H.  Norton:  Elements  of  Geology,  p.  448. 


382 


HISTORICAL  GEOLOGY 


INDEX 


Acadian  series,  57. 

Acidaspis,  101. 

Actinopteriate,  135. 

Adirondack  Mountains,  42-45,  81, 
296,  332. 

Africa,  89,  112,  132,  152,  168,  188, 
189,  210,  211,  225,  255,  305,  307, 
308,  372. 

Agassiz,  L.,  140. 

Age,  31. 

Alabama,  112,  122,  126,  164,  169, 
236-237,  240-241,  248,  286,  287. 

Alaska,  9,  128,  144,  147,  ICO,  163, 
169,  181,  183,  204-205,  212,  220, 
221,  248,  256,  284,  289,  330,  341, 
366,  371. 

Albian  formation,  237. 

AlgaB,  11,  54,  71-72,  91,  132-133,  170. 

Algonkian  (see  also  Proterozoic) 
period,  32,  42;  rocks,  47-49; 
subdivisions,  42,  49;  correlation, 
51;  distribution  of  rocks,  53; 
foreign,  53. 

Allegheny  series,  158,  161-162. 

Allen,  J.,  174. 

Allosaurus,  270. 

Alps,  132,  187,  210,  255,  305,  306, 
307,  308,  368,  372. 

Amber,  fossils  in,  4,  316. 

Ambonychia,  96. 

Ammonoids,  98-99,  135,  156-157, 
175,  191,  214,  230,  258. 

Ammonites,  13,  99,  230,  258,  260, 
314. 

Amceba,  14. 

Amphibians,  13,  21;  Devonian,  142; 
Mississippian,  157;  Pennsylvanian, 
173,  177-179;  Permian,  191,  193; 
Triassic,  215;  Jurassic,  232;  Cre- 
taceous, 261;  Tertiary,  317. 

Ancyloceras,  260. 


Andes  Mountains,  210,  249,  255,  309. 

Angiosperms,  11,  13,  170,  228,  256- 
257. 

Animals,  classification,  10,  11,  13-22; 
earliest  forms,  70-71. 

Animikean,  42,  49. 

Antarctica,  329,  368. 

Anthozoans,  13,  15,  73,  92-93,  114, 
228. 

Anthrapalsemon,  176. 

Ants,  232. 

Apalachicola  formation,  282,  287. 

Apennine  Mountains,  306,  307,  308, 
309. 

Appalachia,  62;  Cambrian,  65;  Or- 
dovician,  84;  Silurian,  108;  Devo- 
nian, 128;  Mississippian,  148; 
Permian,  185-186;  Paleozoic,  195- 
196;  Triassic,  206;  Cretaceous, 
244,  276. 

Appalachian  Mountain  district,  Cam- 
brian, 58-59,  63;  Ordovician,  81; 
Silurian,  105-107,  110;  Devonian, 
121-126,  128,  130;  Mississippian, 
144-148;  Pennsylvanian,  158-166; 
Permian,  181-187;  Paleozoic,  195- 
197;  Triassic,  203,  206;  Creta- 
ceous, 251-252;  Tertiary,  292, 
296-298. 

Appalachian  Revolution,  183-187, 
197. 

Aptian  formation,  237. 

Aquia  formation,  282. 

Arachnids,  13,  21,  76,  100,  116,  118, 
136,  157,  175-176,  191. 

Arbuckle  Mountains,  150. 

Archean,  period,  32;  rocks,  40-41; 
subdivisions,  41-42;  correlation  of 
rocks,  42-43;  distribution  of  rocks, 
44-45;  foreign,  45-46;  economic 
products,  46. 


384 


INDEX 


Archeocyathus,  73. 

Archeopteryx,  234. 

Archeozoic  era,  32,  40-46;  life  of, 
46;  climate,  46. 

Archimedes,  156. 

Arctic  Islands,  79,  104,  106,  112,  121, 
122,  225. 

Argentina,  68,  89,  152,  188,  210,  306, 
308,  309. 

Arikaree  formation,  282,  288. 

Arizona,  53,  65,  84,  128,  181,  213, 
220,  221,  276,  304. 

Arkansas,  90,  163,  187. 

Armor-fishes,  13,  21. 

Arnold,  R.,  290,  294,  295,  297,  36.7. 

Arthrodirans,  138-140,  157. 

Arthropods,  13,  20,  21;  Cambrian, 
75-76;  Ordovician,  99-101;  Silu- 
rian, 116-118;  Devonian,  13G; 
Mississippian,  157;  Pennsylvanian, 
175-177;  Permian,  191;  Triassic, 
215;  Jurassic,  231-232;  Creta- 
ceous, 261;  Tertiary,  314-316. 

Artiodactyls,  319,  321-322. 

Arundel  formation,  237,  240. 

Asia,  152,  168,  188,  210,  225,  227, 
255,  305,  306,  307,  308. 

Asteroids,  13,  17,  93. 

Asterozoans,  13,  17,  115,  134,  156, 
174,  191,  213,  229. 

Augusta  series,  143. 

Ausable  Chasm,  62. 

Austin  formation,  237,  242,  246. 

Australia,  10,  46,  68,  89,  92,  112,  132, 
152,  153,  168,  188,  190,  200,  210, 
225,  227,  255,  256,  306,  372. 

Austria,  132. 

Baculites,  99,  258,  260. 
"Bad  Lands,"  296,  303. 
Barrande,  J.,  97,  115. 
Barremian  formation,  237. 
Barrows  and  Blackwelder,  34,  118. 
Bassler,  R.  S.,  94. 
Bavaria,  46,  .227,  234. 
Becraft  formation,  121. 
Bedford  limestone,  153,  154. 
Beecher,  C.  E.,  101. 


Beekmantown  formation,  78. 

Bees,  232. 

Beetles,  232. 

Belemnites,  215,  231,  314. 

Belemnoteuthis,  231. 

Belgium,  120,  152,  305,  309. 

Berkey,  C.  P.,  87,  251-252. 

Berkshire  Hills,  86,  87,  250,  332. 

Berry,  E.  W.,  312. 

Big  Blue  series,  180,  181. 

Billings,  E.,  93. 

Birds,  13,  22;  Jurassic,  234-235; 
Cretaceous,  262;  Tertiary,  317. 

Bisons,  371. 

Black  Hills,  82,  147,  220,  243. 

Black  Lake,  351. 

Black  River  formation,  78. 

Black  River  Valley,  332,  336-337. 

Blackwelder,  E.,  33. 

Blackwelder  and  Barrows,  34,  118. 

Blake,  J.  H.,  21. 

Blanco  formation,  282,  289. 

Blastoids,  13,  16,  17,  93,  114,  134, 
155,  173. 

Bohemia,  67,  152,  190,  307,  312. 

Boulder  clay,  339. 

Brachiopods,  13,  19,  53,  73-74,  94- 
95,  116-117,  134-135,  156,  174, 
191,  214,  229,  230. 

Branchiosaurs,  178.  -v 

Branner,  J.  C.,  297. 

Brazil,  53,   168,   188,  189,   190,  255, 

306. 

Breuil,  379,  380. 
Bridger  formation,  282,  287. 
Brigham,  A.  P.,  34,  352. 
British  Columbia,  53,  59,  144,  204, 
205,  209,  220,  221,  223,  243,  248, 
250,  256,  276,  284. 

British  Isles  (see  also  England),  56, 
89,  92,  103,  111,  112,  131,  151,  187, 
227,  305,  309,  310,  371. 
Brittany,  67. 
Brittle-stars,  13,  17. 
Brogniart,  A.  T.,  177. 
Bronteus,  101. 
Brontotherium,  318. 
Brooks,  W.  K.,  70. 


INDEX 


385 


Brooksella,  73. 

Broom,  192. 

Bryophytes,  11,  133,  153,  170. 

Bryozoans,    13,    18-19,   94,   115-116, 

134,  156,  174,  191,  214,  229. 
Bumastus,  101. 
Bunter  series,  201,  210. 
Butterflies,  21,  232. 

California,  Mississippian,  147;  Penn- 
sylvanian,  163;  Permian,  181,  183; 
Triassic,  201,  204,  212;  Jurassic, 
220,  221,  223,  225,  227;  Creta- 
ceous, 237,  243,  246,  248,  256,  276; 
Tertiary,  282,  289,  290,  297,  300, 
303,  310,  312,  313;  Quaternary, 
331,  366,  367,  372. 

Calkins,  F.  C.,  303. 

Callithamnopsis,  91. 

Caloosahatchee  formation,  282,  287. 

Calvert  formation,  282. 

Calvin,  S.,  257. 

Calymmene,  101,  115. 

Cambrian  period,  32,  56-76;  origin 
of  name,  56;  subdivisions,  57; 
distribution  of  rocks,  57-59;  char- 
acter of  rocks,  59;  thickness,  59; 
igneous  rocks,  59,  61;  physical 
history,  61-67;  length  of  time,  65; 
foreign,  67-68;  climate,  68-69; 
glaciation,  68;  economic  products, 
69;  life  of,  69-76. 

Camel,  evolution  of,  321-322. 

Campbell,  M.  R.,  62,  187. 

Canada  (see  also  various  provinces), 
42,  44,  45,  53,  55,  65,  82,  84,  106, 
108,  121,  128,  148,  197,  287,  332, 
350,  358. 

Canadian  series,  78. 

Capitan,  380. 

Carboniferous  (see  Mississippian  and 
Pennsylvanian). 

Carbonization,  4. 

Cardiola,  96. 

Carnivores,  319,  325-326. 

Carpathian  Mountains,  307. 

Cartailhac,  379,  380. 

Caryocrinus,  114. 


Cascade  Mountains,  220,  223,  277, 

289,  300,  301,  304. 
Castle  Hayne  formation,  282. 
Casts,  4. 
Catopterus,  216. 

Catskill  formation,  120,  124,  130. 
Catskill  Mountains,  332. 
Caucasus  Mountains,  307,  308-309, 

368. 

Cayugan  series,  103,  106-107,  113. 
Cenomanian  formation,  237. 
Cenozoic  era,  32,  281-381. 
Centipedes,  13,  21. 
Cephalopods,   13,  20-21,  75,  97-99, 

117,   135-136,   156-157,   175,   191, 

214-215,    230-231,    258,    260-261, 

314. 

Ceratites,  99,  214. 
Ceraurus,  101. 
Cereals,  313. 
Cetaceans,  319,  325-326. 
Chamberlain,  C.  J.,  226. 
Chamberlin,  T.  C.,  25,  37,  355,  363. 
Chamberlin   and   Salisbury,    28,    33, 

37,  49,  61,  71,  75,  115,  137,  150, 

155-156,   159,  174,  189,  192,  211, 

326,  358,  363-364. 
Champlain  sea,  364,  365. 
Champlain  Valley,  297,  332,  336,  348, 

364. 
Chautauquan  series,  120,  124;   time, 

130. 

Chemung  formation,  120,  124,  130. 
Chester  series,  143,  147,  153;    time, 

148. 

Chico  formation,  237,  243. 
Chili,  152,  210. 
China,  46,  68,  89,  112,  132,  168,  169, 

188,  255. 

Choctawhatchee  formation,  282,  287. 
Choptank  formation,  282. 
Chouteau  series,  143. 
Chronology,  of  earth,  7. 
Chuar  group,  51. 
Cimarron  series,  180,  181. 
Cincinnati  Anticline,  88,  148. 
Cincinnati  series,  78. 
Citronelle  formation,  282,  287. 


386 


INDEX 


Cladoselache,  139. 

Claiborne  formation,  282. 

Clams,  13,  20. 

Claosaurus,  272. 

Clark,  W.  B.,  23,  220,  240-241,  292. 

Clarke,  J.  M.,  8,  116,  128,  129,  134, 
137. 

Classification,  animals  and  plants, 
10-22;  geologic  time,  31-32. 

Clear  Fork  series,  180. 

Cleland,  H.  F.,  33. 

Climacograptus,  92. 

Climate,  past  conditions,  9;  see  also 
the  different  periods. 

Clinton  formation,  103,  105,  106,  107, 
108,  112. 

Clitambonites,  95. 

Coal,  Pennsylvanian,  158-162;  origin 
of,  164;  areas  in  North  America: 
Permian,  189,  190;  Triassic,  212; 
Jurassic,  227;  Cretaceous,  256. 

Coal  Measures,  158,  161,  177. 

Coastal  Plain,  Atlantic,  237-244,  251- 
252,  256,  275,  276,  282,  284-286, 
290-292,  317,  365-366. 

Coastal  Plain,  Gulf,  237-245,  256, 
275,  276,  282,  284,  287,  290,  292, 
293,  365-366. 

Coast  Range  Mountains,  220,  223, 
243,  248,  277,  289,  290,  297,  299- 
300,  304. 

Coast  Range  Revolution,  300. 

Cobalt,  46. 

Cobleskill  formation,  103,  107,  110. 

Coccosteus,  139. 

Coe,  18. 

Ccelenterates,  13,  15;  Cambrian,  72- 
73;  Ordovician,  91-92;  Silurian, 
114;  Devonian,  133-134;  Missis- 
sippian,  155;  Pennsylvanian,  173; 
Permian,  191;  Triassic,  213;  Ju- 
rassic, 228;  Cretaceous,  258;  Ter- 
tiary, 313. 

Coeymans  formation,  121. 

Coleman,  A.  P.,  55. 

Colorado,  102,  128,  147,  164,  181, 
190,  220,  242,  243,  246,  287,  288, 
310,  316. 


Colorado  formation,  237,  242;  time, 
246. 

Colorado  Plateau,  301,  304. 

Columbia  formation,  365. 

Columbian  Plateau,  303-304. 

Comanchean,  236. 

Conemaugh  series,  158,  161-162. 

Conifers,  11,  13,  172,  190,  212,  213, 
227,  256,  257. 

Connecticut  Valley,  5,  203-204,  208- 
209,  212,  216-217,  270,  297. 

Cope,  E.  D.,  319. 

Copper,  55,  212. 

Corals  (see  also  Anthozoans),  13,  16, 
73,  92-93,  113-114,  133-134,  154- 
155,  173,  191,  228,  258. 

Cordaites,  11,  12,  172,  175,  190,  212. 

Cordillera,  195-197. 

Correlation  of  rock  formations,  23-27. 

Correlation,  inorganic  criteria,  23- 
26;  paleontological  criteria,  26-27. 

Corydaloides,  177. 

Couch,  233. 

Crabs,  13,  20,  231,  233,  261,  314. 

Creodonts,  325-326. 

Cretaceous  peneplain,  250-251,  296. 

Cretaceous  period,  32,  236-273; 
origin  of  name,  236;  subdivisions, 
237;  distribution  of  rocks,  236-240; 
character  of  rocks,  240-244;  thick- 
ness, 243;  igneous  rocks,  243-244; 
physical  history,  244-252;  foreign, 
252-255;  climate,  255;  economic 
products,  256;  life  of,  256-263. 

Crinoids,  13,  16-17,  114-115,  134, 
155,  173-174,  191,  213,  229,  258. 

Crioceras,  260. 

Crocodiles,  22,  234,  273. 

Croll's  hypothesis,  361-363. 

Crustaceans,  13,  20-21,  53,  75-76, 
99,  100,  101,  117-118,  157,  191, 
215,  231,  314. 

Cryptogams,  11,  91,  154,  170,  190. 

Cryptozoon,  71-72. 

Gushing,  H.  P.,  72. 

Cuttle-fishes,  13,  20. 

Cycads,  11,  12,  172,  190,  226-228, 
256,  257. 


INDEX 


387 


Cycadeoidea,  227. 
Cycadofilices,  11,  12,  172-174. 
Cyphaspis,  115. 
Cyrtoceras,  97-99. 

Cystoids,  13,  16-17,  73,  93,  114,  134, 
155. 

Dakota,    formation,    237,    242,    256, 

277;    time,  246. 
Dall,  W.  H.,  292. 
Danian  formation,  237. 
Dana,  J.  D.,  11,  33,  34,  312,  381. 
Darton,  N.  H.,   182,  205,  227,  249, 

259,  296. 
Darwin,  C.,  3. 
Dawson,  387. 
Dean,  B.,  137,  138. 
Decapods,  215,  231-232,  261. 
Deccan,  255. 
Deiphon,  115. 
De  Lapparent,  A.,  89,  111,  131,  151, 

167,  189,  211,  224,  253,  254,  306, 

307,  308. 
Delaware,  240. 
Delaware  River,  297. 
Deposits,  land,  5;   river  and  lake,  6; 

marine,  6. 
Devonian,    period,    8,    32,    120-142; 

origin  of  name,  120;    subdivisions, 

120-121;    rock   distribution,    121- 

124;    character  of  rocks,  122-125; 

thickness,  125;  igneous  rocks,  125; 

physical  history,  125-130;  foreign, 

131-132;    climate,   132;    economic 

products,  132;   life  of,  132-142. 
Diatoms,  133,  311-312. 
Dibranchs,  13,  20,  215,  231,  314. 
Dicotyledons,  11,  13. 
Dictyonema,  92. 
Didymograptus,  92. 
Dikellocephalus,  57,  75. 
Dinosaurs,   215,  234,   263^  266-271, 

311. 

Dioon,  226. 
Diplodocus,  268. 
Diplograptus,  92. 
Diplomystus,  316. 
Dipnoans,  138-139,  157,  215,  232. 


Dipterus,  139. 

Dismal  Swamp,  164. 

Dcedicurus,  370. 

Dogger  series,  219. 

Dolomite,  69. 

Double  Mountain  series,  180. 

Drift,  glacial,  329,  337. 

Drumlins,  339-340. 

Du  Bois,  375. 

Duckworth,  W.  H.,  376,  377. 

Dunkard  series,  180-181. 

Eagle  Ford  formation,  237-242. 

Eanthropus,  378-379. 

Earth,  age  of,  1 ;  physical  geography 
of,  1;  chronology,  7;  origin,  35-39; 
pre-geologic,  35. 

Earth's  history,  summary  of  stages, 
39. 

Eastman-Zittel,  book  by,  34. 

Echinoderms,  13,  15-17;  Cambrian, 
73;  Ordovician,  93;  Silurian,  U4r- 
115;  Devonian,  134;  Mississip- 
pian,  155-156;  Pennsylvanian, 
173;  Permian,  191;  Triassic,  213- 
214;  Jurassic,  229-230;  Creta- 
ceous, 258;  Tertiary,  313. 

Echinoids,  13,  17,  18,  93,  115,  156, 
174,  191,  213-214,  229-230,  258. 

Echinozoans  (see  also  Echinoids),  13, 
17,  18,  134. 

Edentates,  370-371. 

Edwards  and  Haime,  113. 

Elephant,  evolution  of,  322-325. 

Elephas,  323. 

Emergence,  of  land,  29. 

Emerson,  B.  K.,  203,  208. 

Enaliosaurs,  215,  234,  263-266. 

Endogenous  plants,  12. 

England  (see  also  British  Isles),  9, 
115,  120,  152,  210,  219,  225,  231, 
236,  254,  309,  378. 

Eocene  series,  281-288. 

Eohippus,  319-321. 

Epoch,  31. 

Equisetae,  11,  12,  133,  154,  171,  173, 
190,  212,  227,  256. 

Equus,  318,  320-321. 


388 


INDEX 


Era,  31,  32. 

Brian  series,  120,  122,  124;  time, 
128. 

Erratics,  329,  338-339. 

Eryops,  173,  178. 

Esopus  formation,  121. 

Eucalyptocrinus,  114. 

Eucrustaceans,  13,  76,  100,  117-118, 
136,  157,  175-176,  215,  231. 

Euproops,  176. 

Europe,  Cambrian,  67-68;  Ordovi- 
cian,  88-89;  Silurian,  111-112; 
Devonian,  128,  130-131;  Missis- 
sippian,  151-152;  Pennsylvanian, 
167-169;  Permian,  187-188,  190, 
194,  197,  200;  Triassic,  210-211; 
Jurassic,  224-225;  Cretaceous,  237, 
252-255;  Tertiary,  305-309,  310, 
313;  Quaternary,  368,  371,  375- 
381. 

Eurypterids,  13,  76,  100,  116,  118, 
136,  177,  191. 

Eurypteris,  116. 

Eutaw  formation,  237,  241. 

Exogenous  plants,  12. 

Exogyra,  230,  259. 

Fairchild,  H.  L.,  339. 

Ferns,  11,  12,  133,  154,  172,  190,  212, 

227,  256. 

Filices,  11,  12,  172. 
Finger  Lakes,  336,  337,  350. 
Finland,  46,  53. 

Fishes,  13,  21;  Silurian,  119;  Devo- 
nian, 137-142;  Mississippian,  157; 

Pennsylvanian,  177;  Permian,  191; 

Triassic,    215;     Jurassic,  232-233; 

Cretaceous,   261;     Tertiary,    316- 

317. 

Flagstones,  132. 
Flies,  13,  232. 

Florida,  284,  287,  292,  294,  310. 
Florissant  formation,  282,  288. 
Footprints,  fossil,  5,  203,  208,  216- 

217. 
Foraminifers,  13,  14,  15,  71-72,  91, 

133,  154,  172-173,  190,  228,  257, 

258,  313. 


Forbesiocrinus,  155. 

Fordilla,  74. 

Fort  Union  formation,  282,  287. 

Fossils,  significance,  3,  6;  preserva- 
tion, 4;  rocks  in  which  found,  5. 

Fraas,  E.,  213,  265. 

France,  46,  53,  67,  113,  132,  152,  187. 
190,  236,  254,  305,  307,  309,  371, 
378,  380. 

Frankfort  formation,  78,  88. 

Fredericksburg,  formation,  237,  242, 
276;  time,  246. 

Frogs,  13,  22. 

Fungi,  11. 

Ganoids,  138-140,  157,  215-216,  232, 
261. 

Gas,  in  Ordovician  strata,  90;  in 
Silurian,  113;  in  Devonian,  132; 
in  Mississippian,  153;  in  Pennsyl- 
vanian, 169. 

Gastropods,  13,  20,  74-75,  96-97; 
117,  135-136,  156,  175,  191,  214, 
230,  258,  313,  315. 

Gaudry,  A.,  326. 

Geikie,  A.,  23,  33. 

Geikie,  J.,  368. 

Genesee  formation,  120,  124. 

Geological  divisions,  32. 

Geologic  and  human  history  com- 
pared, 32-33. 

Geologic  time,  classification,  31-32. 

Georgia,  314. 

Georgian  series,  57. 

Germany,  Proterozoic,  53;  Cam- 
brian, 67;  Devonian,  132;  Mis- 
sissippian, 152;  Permian,  187,  190; 
Triassic,  201,  210;  Jurassic,  219, 
225;  Cretaceous,  256;  Tertiary, 
305,  306,  307,  309,  310,  316; 
Quaternary,  368,  375,  377. 

Gibbes,  317. 

Gilbert,  G.  K.,  354,  367. 

Glacial  boulders  (see  erratics). 

Glaciation,  Proterozoic,  55;  Cam- 
brian, 68;  Mississippian,  153; 
Permian,  188-190;  Quaternary, 
328-364,  368. 


INDEX 


389 


Glacial  epoch,  328-364;  fact  of,  328- 
329;  ice  extent  and  centers,  329- 
331;  movement  and  depth  of  ice, 
331-333;  successive  ice  invasions, 
333-334;  driftless  areas,  334;  ice 
erosion,  334-337;  ice  deposits, 
337-341;  loess,  341;  Great  Lakes 
history,  342-349;  other  existing 
lakes,  348,  350;  extinct  lakes,  351- 
352;  drainage  changes,  352-356; 
advantages  and  disadvantages, 
357-358;  duration,  358;  time 
since,  359-360;  cause  of,  360-364; 
in  Europe,  368. 

Glacier  National  Park,  33. 

Glyptodonts,  369,  371. 

Glyptocrinus,  93. 

Gold  deposits,  in  Jurassic,  225-226; 
in  Tertiary,  310-311. 

Goldfuss,  A.,  229. 

Goniatites,  99,  135-136,  156-157, 
175. 

Grabau,  A.  W.,  34. 

Grammy  sia,  135. 

Grand  Canyon  of  Arizona,  51-52, 
147,  301. 

Granger,  W.,  288. 

Granite,  Archean,  46. 

Graphite,  46,  54. 

Graptolites,  13,  15,  72-73,  91-92, 
114,  133,  155. 

Grasses,  313. 

Grasshoppers,  13,  21,  232. 

Great  Basin,  82,  104,  107,  181,  183, 
289,  301. 

Great  Lakes,  106;  history  of,  342- 
349. 

Great  Salt  Lake,  366. 

Greenbrier  formation,  143,  147. 

Greenland,  255,  313,  329. 

Green  Mountains,  86,  87,  250,  332. 

Green  River  formation,  282,  287. 

Green  sands,  256. 

Grenville  series,  42-43. 

Ground-sloths,  370. 

Group,  31,  32. 

Gryphea,  230. 

Guelph  formation,  103-106. 


Guettard,  J.,  113. 

Guth,  F.  B.,  81. 

Gymnosperms,  11,  12,  133,  154,  170, 
172,  190,  212-213,  256. 

Gypsum  quarries,  Silurian,  113;  Per- 
mian, 190;  Triassic,  212. 

Haime  and  Edwards,  113. 

Hall,  J.,  92,  96,  97,  114,  115,  136, 
137,  155. 

Halysites,  113.. 

Hamilton  formation,  120,  122-124, 
133 

Haug,  E.,  33. 

Helderbergian  series,  121-122;  time, 
125-126. 

Helioceras,  260. 

Heliolites,  113. 

Hemiaster,  230. 

Hesperornis,  262. 

Hexacoralla,  93,  191,  213,  226. 

Highlands  of  the  Hudson,  87,  298. 

Hill,  R.  T.,  229,  230,  242,  259. 

Himalaya  Mountains,  188,  210,  225, 
255,  308,  308,  309. 

Hitchcock,  E.,  217. 

Holland,  305. 

Holothuroids,  13,  17,  18,  73,  93. 

Holyoke  Range,  208,  209,  277. 

Homalonotus,  137. 

Homo  heidelbergensis,  375-376. 

Homo  primigenius,  373-374. 

Homo  sapiens,  373-374. 

Horse,  evolution  of,  319-321. 

Horse-shoe  Crabs,  13,  117. 

Horsetown  formation,  237,  243. 

Howes,  19. 

Hudson  River,  279,  298,  299,  355. 

Hudson  Valley,  108,  112,  297,  298, 
332,  348,  364. 

Human  and  geologic  history  com- 
pared, 32-33. 

Hungary,  227. 

Hunter,  117. 

Hunter,  G.  W.,  11. 

Huronian,  42,  49,  50,  55. 

Hydrozoans,  13,  15,  72-73,  91-92. 

Hypsocormus,  233. 


390 


INDEX 


Ice  Age  (see  Glacial  epoch). 

Iceland,  307. 

Ichthyornis,  262. 

Ichthyosaurs,  263-265. 

Idaho,  220,  366. 

Illinois,  90,  105,  122,  153,  164,  169, 

334,  341,  356. 

India,  46,  53,  68,  89,  188,  225,  255. 
Indiana,  90,  105,  107,  130,  153,  154, 

155,  156,  169,  341. 
Inoceramus,  259. 
Insectivores,  319,  325. 
Insects,   13,  21,   100,   119,   136,  157, 

173,  177,  191,  215,  232,  314,  315, 

316. 
Iowa,  60,  90,  123,  150,  155,  169,  181, 

190,  256,  334,  341,  371. 
Ireland,  307. 
Iron   ore,    Archeozoic,    46;     Protero- 

zoic,  55;    Silurian,  112;    Pennsyl- 

vanian,  169. 
Isotelus,  101. 
Italy,  305,  306,  309. 

Jackson  formation,  282. 

Jacksonville  formation,  282,  287. 

Japan,  46,  210,  225,  255,  308. 

Java,  327,  375. 

Jelly-fishes,  13. 

Johnson,  B.  L.,  291-292. 

Jordan  and  Kellogg,  34. 

Jura  Mountains,  219. 

Jurassic  period,  32,  219-235;  origin 
of  name,  219;  subdivisions,  235; 
distribution  of  rocks,  219-220; 
character  of  rocks,  220-221; 
thickness,  221;  igneous  rocks,  221; 
physical  history,  221-224;  foreign, 
224;  climate,  225;  economic  prod- 
ucts, 225-226;  life  of,  227-235. 

Kames,  340. 

Kansas,  153,  169,  180-183,  190,  242, 

256,  289. 

Kaskaskia  series,  143. 
Kayser,  E.,  33. 
Keith,  A.,  83. 
Kellogg  and  Jordan,  34. 


Kentucky,  122,  133,  169,  371. 

Kettle-holes,  338. 

Keuper  series,  201,  210. 

Kewatin,  42-43. 

Keweenawan,  42,  49,  50,  55. 

Keyes,  C.  R.,  150. 

Kinderhook  series,  143,  146. 

Klamath  Mountains,  223. 

Knight,   C.  R.,  264,  267,  268,   269, 

270,  321,  323. 
Knowlton,  F.  H.,  213,  257. 
Knoxville  formation,  237,  243. 
Kootenai  formation,  237,  242,  246. 

Labrador,  84. 

Labyrinthodonts,  178-179. 

La  Chapelle,  Men  of,  374,  378. 

Lafayette  formation,  282,  286,  291- 

292. 

Lake  Agassiz,  351-352. 
Lake  Algonquin,  347-348. 
Lake  Bonneville,  366-367. 
Lake  Champlain,  350. 
Lake  Chicago,  343-345. 
Lake  George,  350. 
Lake  Iroquois,  347-348. 
Lake  Lahontan,  367. 
Lake  Maumee,  343-344. 
Lake  Saginaw,  344-345. 
Lake  Superior  district,  42,  46,  48-50, 

55,  58,  84. 

Lake  Warren,  345,  347. 
Lake  Whittlesey,  344-345. 
Lamp-shells,  13. 
La  Place,  P.,  36. 
Lapworth,  C.,  77. 
Laramie  formation,  237,  243;    time, 

246. 

Laramide  Range,  249. 
Lassen  Peak,  304,  305,  366. 
Laurentian,  42-43. 
Lawson,  A.,  54. 
Lead  ore,  90. 
Le  Conte,  J.,  33,  40,  98,  100,  117,  141, 

176,  177,  194,  233,  234-235,  257, 

260,  261,  266,  313,  315-316,  361- 

362,  367,  375,  377-378. 
Leith  and  Van  Hise,  41,  48,  55. 


INDEX 


391 


Lemuroids,  327. 

Lepidodendrons,  170,  173,  190. 

Leptomites,  73. 

Leverett,  F.,  343,  344,  345,  346,  355, 

356. 

Lias  series,  219;    time,  224. 
Lignite,  310. 

Limestone  quarries,  90,  112,  153,  256. 
Limnoscelis,  173. 
Lindgren,  W.,  220. 
Lingula,  95. 
Lingulella,  74. 
Linnaeus,  C.,  113. 
Lithographic  limestone,  225,  227. 
Little  Falls  formation,  57. 
Lizards,  13,  216,  234,  273. 
Lobsters,  13,  20,  215,  231. 
Lockport  formation,  103,  106. 
Long  Island,  338,  340. 
Lonsdaleia,  154. 
Lorraine  formation,  78,  82. 
Louisiana,  256. 

Loup  Fork  formation,  282,  288. 
Lower     Carboniferous     period     (see 

Mississippian) . 
Loxonema,  136. 
Lucas,  F.  A.,  269. 

Lull,  R.  S.,  271,  323,  324,  325,  371. 
Lung-fishes,  138-140. 
Luther,  D.  D.,  129. 
Lycopods,  11,  12,  133,  154,  170-171, 

190,  212. 
Lyell,  C.,  27,  28,  281. 

Maclurea,  96. 

Macrurans,  215,  231-232. 

Madagascar,  372. 

Magothy  formation,  237,  240-241. 

Maine,  107,  122,  130,  299,  350. 

Malm  series,  219. 

Mammals,  10,  13,  22;   Triassic,  217; 

Jurassic,    235;     Cretaceous,    263; 

Tertiary,     317-327;      Quaternary, 

369-381. 

Mammoth  coal  bed,  166. 
Mammoths,  4,  322-323,  371. 
Man,  13,  22,  327;   evolution  of,  372- 

381. 


Manasquan  formation,  237,  241. 
Manganese  ore,  90. 

Manitoba,  106,  123. 

Manlius  formation,  103,  110. 

Mantell,  G.,  231. 

Manticoceras,  136. 

Map  of  United  States,  Physiographic 
provinces,  382. 

Maps  showing  rock  distribution,  pre- 
Cambrian,  44;  Cambrian,  58; 
Ordovician,  79;  Silurian,  105; 
Devonian,  123;  Mississippian  and 
Pennsylvanian,  145;  Mississippian, 
146;  Pennsylvanian,  159;  Triassic 
and  Jurassic,  202;  Lower  Creta- 
ceous, 238;  Upper  Cretaceous,  239; 
Lower  Tertiary,  283;  Upper  Ter- 
tiary, 285;  Cenozoic  volcanic 
rocks,  302. 

Maps  showing  paleogeography  of 
North  America,  Lower  Cambrian, 
64;  Middle  and  Upper  Cambrian, 
66;  Middle  Ordovician,  85;  Silu- 
rian, 109;  Early  Devonian,  126; 
Middle  Devonian,  127;  Missis- 
sippian, 149;  Pennsylvanian,  165; 
Permian,  184;  Triassic,  207;  Ju- 
rassic, 222;  Lower  Cretaceous,  245; 
Upper  Cretaceous,  247;  Eocene- 
Oligocene,  293;  Miocene,  295. 

Maps  showing  paleogeography  of 
Europe,  Ordovician,  89;  Silurian, 
111;  Devonian,  131;  Mississip- 
pian, 151;  Pennsylvanian,  167; 
Permian,  189;  Triassic,  211;  Ju- 
rassic, 224;  Lower  Cretaceous,  253; 
Upper  Cretaceous,  254;  Eocene, 
306;  Miocene,  307;  Pliocene, 
308. 

Marble,  46,  90. 

Marcellus  formation,  120,  122-124, 
133. 

Mariopteris,  171. 

Mariposa  slate,  220-221,  223. 

Marsh,  O.  C.,  262,  269,  272,  318,  375. 

Marsupials,  318. 

Martha's  Vineyard,  239. 

Martinez  formation,  282. 


392 


INDEX 


Maryland,  143,  147,  161,  220,  240, 
285,  292. 

Massachusetts  (see  also  Connecticut 
Valley),  163,  197,  203,  204,  208, 
209,  271,  279,  339. 

Mastodons,  322-324,  371. 

Mastodonsaurus,  215. 

Matawan  formation,  237,  241. 

Matherella,  74. 

Matthew,  W.  D.,  92,  320. 

Mauch  Chunk  shales,  143,  147,  148. 

Medina  formation,  103-104,  113. 

Meek,  F.  B.,  93,  175,  176,  260. 

Megatherium,  370. 

Merced  formation,  282. 

Merostomes,  13,  117. 

Mesohippus,  320. 

Mesopithecus,  326. 

Mesozoic  era,  32,  201-280;  reptiles, 
263-273;  summary  of  history, 
274-280;  rocks,  274-275;  physical 
history,  275-277;  climate,  277-278; 
organic  history,  278-280;  sum- 
mary of  life,  278-279. 

Mexico,  183,  219,  221,  226,  242,  246, 
288,  294. 

Michigan,  55,  106,  110,  112,  113,  122, 
128,  130,  146,  148,  153,  169,  200. 

Microsaurs,  178-179. 

Midway  formation,  282. 

Minnesota,  45,  55,  350,  359. 

Miocene  series,  281-282,  284,  286- 
290. 

Mississippian  period,  32,  143-157; 
origin  of  name,  143;  subdivisions, 
143-144;  rock  distribution,  144- 
147;  character  of  rocks,  145-147; 
thickness,  147;  igneous  rocks,  147; 
physical  history,  148-151;  foreign, 
151-152;  climate,  153;  economic 
products,  153;  life  of,  153-157. 

Mississippi  Valley,  Archean,  45; 
Algonkian,  53;  Cambrian,  59,  65; 
Ordovician,  81-82,  84,  88,  90; 
Silurian,  104-107;  Devonian,  122- 
126,  128;  Mississippian,  143-150; 
Pennsylvanian,  158-161,  163-165; 
Permian,  181,  185,  187;  Paleozoic, 


194-196;  Triassic,  201;  Tertiary, 
299;  Quaternary,  330-334,  357. 

Missouri,  58,  82,  84,  90,  105,  106, 
122,  123,  153,  334. 

Missouri  River,  356. 

Mohawkian  series,  78. 

Mohawk  Valley,  82,  297,  332,  348, 
352,  353,  354. 

Molds,  4. 

Molluscoids,  13,  18,  19;  Cambrian, 
73-74;  Ordovician,  94^95;  Silu- 
rian, 115-116;  Devonian,  134-135; 
Mississippian,  156;  Pennsylvanian, 
174;  Permian,  191;  Triassic,  214; 
Jurassic,  229-230;  Cretaceous,  258; 
Tertiary,  313.  . 

Mollusks,  13,  20;  Cambrian,  75; 
Ordovician,  94-99;  Silurian,  117; 
Devonian,  135-136;  Mississippian, 
156-157;  Pennsylvanian,  175;  Per- 
mian, 191;  Triassic,  214-215; 
Jurassic,  230-231;  Cretaceous, 
258-261;  Tertiary,  313-315. 

Monkeys,  326-327. 

Monmouth  formation,  237,  241. 

Monocotyledons,  11,  13,  228. 

Monongahela  series,  158,  161-162. 

Monotremes,  318. 

Montana,  153,  200,  220,  250,  287, 
310,  331. 

Montana  formation,  237,  242-243. 

Monterey  formation,  282,  289,  300. 

Moraines,  338-339. 

Morrison  formation,  237,  242,  246. 

Mosasaurs,  262,  263,  266-267. 

Moulton,  F.  R.,  34,  37-38. 

Mount  Lassen,  eruptions,  304-305. 

Mount  Shasta,  305,  366. 

Murchison,  R.,  56,  77,  120,  180. 

Muschelkalk  series,  201,  210. 

Myriapods,  13,  21,  136,  157,  177. 

Nanjemoy  formation,  282. 

Naosaurus,  192. 

Naumann,  215. 

Nautiloids,    98-99,    117,    136,    156, 

175,  191,  214,  230,  258,  314. 
Nautilus,  13,  20-21,  98,  99,  191,  314. 


INDEX 


393 


Navarro,  formation,  237,  242;    time, 

246. 

Neanderthal  Man,  374,  375,  377. 
Nebraska,   181,  249,  256,  288,  289, 

296. 

Nebula,  36-38. 
Nebular  hypothesis,  36-37. 
Neocomian  formation,  237. 
Neolemus,  76. 
Neolithic  age,  374. 
Neolithic  Man,  381. 
Neumayr,  M.,  232. 
Nevada,  53,  59,  122,  125,  128,  204, 

220,  221,  224,  303,  310. 
Newark  series,  201,  203-204,  206-208, 

212,  221,  276. 
Newberry,  J.  S.,  216. 
New  Brunswick,  63,  82,  88,  107,  122, 

125,  126,  128,  130,  147,  160,  163, 

169,  181-183. 
New  England,  45,  57,  59,  81-82,  86, 

90, 195,  251-252,  297,  332,  334,  340, 

350,  358. 

Newfoundland,  45,  53,  57,  131,  187. 
New  Jersey,  203,  223,  240,  256. 
New  Mexico,  164,  181,  183,  190,  304, 

366. 

"New  Red  Sandstone,"  203. 
New  Scotland  formation,  121. 
Newsom,  J.  F.,  297. 
New  York,  Archeozoic,  42-46;  Cam- 
brian, 57,  58,  62,  65,  67,  69;  Ordo- 

vician,  77-78,  80,  82,  86,  87,  88; 

Silurian,   103-108,   110,   112,   115; 

Devonian,  120-124,  128-130,  132; 

Paleozoic,  200;   Triassic,  203,  208; 

Cretaceous,     250-251;      Tertiary, 

297;    Quaternary,  332-340;    345- 

355,  358-359. 
New  Zealand,  89,  132,  152,  188,  210, 

225,  255,  256,  313. 
Niagara  River,  347;   Falls,  354-355, 

359. 

Niagara  formation,  106,  107. 
Niagaran  series,  103-108. 
Nicholson,  H.  A  ,  97,  139. 
Nickel,  46. 
Nipissing  Lakes,  348-349. 


Noble,  L.  F.,  52. 

North  Carolina,  164,  212,  213,  291. 

North  Dakota,  287. 

Norton,  W.  H.,  2,  34,  60,  179,  230, 

231,  263,  303-304,  322,  330,  340, 

354,  355,  368,  375,  381. 
Norway,  68,  368. 
Nova  Scotia,  53,  106-107,  122,  125, 

126,  130,  147,  148,  153,  160,  163, 

164,  169,  181,  183,  200,  201,  203, 

331. 

Nummulina,  313. 
Nummulites,  313. 

Oakville  formation,  282,  287. 

Odontopteryx,  317. 

Oeningen,  315-316,  317. 

Ohio,  88,  90,  106,  110,  112,  153,  169, 
181-182. 

Ohio  River  (Upper),  355-356. 

Oil,  in  Ordovician  strata,  90;  Silu- 
rian, 113;  Devonian,  132;  Mis- 
sissippian,  153;  Pennsylvanian, 
169;  Jurassic,  225;  Cretaceous, 
256;  Tertiary,  310. 

Oklahoma,  58,  82,  86,  106,  122,  153, 
169,  181,  190,  242. 

"Old  Red  Sandstone,"  131-132,  203. 

OleneUus,  57,  75. 

Oligocene  series,  281-284,  286-289. 

Oneida  formation,  103-104,  108. 

Onondaga,  formation,  120,  122;  time, 
128. 

Ontario,  46,  54,  106,  110. 

Oolite  series,  219. 

Ophileta,  96. 

Ophiuroids,  13,  17,  93. 

Orbiculoidea,  95. 

Order  of  Superposition,  7. 

Ordovician  period,  32,  77-102;  origin 
of  name,  77;  subdivisions,  78; 
rock  distribution,  78-81 ;  character 
of  rocks,  81-83;  thickness,  82; 
metamorphism,  82;  igneous  rocks, 
82;  physical  history,  84-88;  for- 
eign, 88-89;  climate,  90;  eco- 
nomic products,  90;  life  of,  90-102. 

Oregon,  220,  221,  223,  289,  300. 


394 


INDEX 


Organisms,  changes  in,  2,  3;   modern 

relations,  10. 
Oriskany,  formation,  121-122;   time, 

126. 

Oriskanian  series,  121-122. 
Ornithopods,  263,  271-272. 
Orthoceras,  97-99. 
Orthodesma,  96. 
Osage    series,   143,   146;     time,   148, 

155. 
Osborn,  H.   F.,   192,  264,  267,  268, 

270,  321,  326. 
Osmeroides,  261. 
Osteolepis,  139. 
Ostracoderms,  13,  21,  119,  137-138, 

157. 

Ostrea,  230,  258-259,  314. 
Oswegan  series,  103-104. 
Oswego  formation,  103,  104. 
Overwash  plain,  338. 
Owen,  R.,  179,  317. 
Oysters,  13,  20,  229,  258,  313-314. 
Ozarkian,  65. 
Ozark  Mountains,  84,  148. 

Paintings,  Paleolithic,  379-380. 

Paleaster,  134. 

Paleasterina,  93. 

Paleogeography,  29-31  (see  also 
maps). 

Paleolithic  Age,  374;  Men,  376-380; 
paintings,  379-380. 

Paleontology,  definition,  3. 

Paleophonus,  117. 

Paleospondylus,  136-137. 

Paleozoic  era,  32,  56-200;  summary 
of  history,  194-200;  rocks,  194; 
physical  history,  195-197;  climate, 
197,  200;  summary  of  life,  198- 
199;  organic  history,  200. 

Palisades,  of  the  Hudson,  208,  277. 

Palms,  312-313. 

Pamelia  formation,  78. 

Panama,  9. 

Paradoxides,  57,  75. 

Pareiasaurus,  192. 

Pascagoula  formation,  282,  287. 

Patagonia,  255. 


Patapsco  formation,  237,  240. 

Patriofelis,  326. 

Patten,  W.,  138. 

Patuxent  formation,  237,  240. 

Peach,  B.  N.,  117. 

Peale,  A.  C.,  250. 

Pelagiella,  74. 

Pelecypods,  13,  19-20,  74-75,  94-96, 
117,  135,  156,  175,  191,  214,  230, 
258-259,  313-315. 

Pelmatozoans,  13,  16,  17,  173. 

Pemphix,  215. 

Pennsylvania,  Ordovician,  90;  Devo- 
nian, 122,  124,  132,  142;  Missis- 
sippian,  143,  145,  147,  150,  153; 
Pennsylvanian,  158,  160-164,  166, 
169;  Permian,  180,  181-182;  Cre- 
taceous, 251;  Quaternary,  355, 
356. 

Pennsylvanian  period,  32,  158-180; 
origin  of  name,  158;  subdivisions, 
158;  rock  distribution,  159-160; 
character  of  rocks,  161-163;  thick- 
ness, 163;  igneous  rocks,  163; 
physical  history,  163-166;  length 
of  time,  166;  foreign,  167-168; 
climate,  168;  economic  products, 
168-169;  life  of,  169-180. 

Pentacrinus,  227. 

Pentamerus,  117,  156. 

Pentrimites,  155. 

Period,  31,  32. 

Perissodactyls,  319-321. 

Permian,  period,  32,  180-193;  origin 
of  name,  180;  subdivisions,  180; 
rock  distribution,  181-182;  char- 
acter of  rocks,  181-182;  thick- 
ness, 182;  igneous  rocks,  182; 
physical  history,  183-188;  foreign, 
187-189;  climate,  189-190;  eco- 
nomic products,  190;  life  of,  191- 
193. 

Persia,  225. 

Peru,  89. 

Petrifaction,  5. 

Pfurtscheller,  16. 

Phacops,  137. 

Phanerogams,  11,  12,  154,  170. 


INDEX 


395 


Phenacodus,  319. 

Phosphate,  132,  311. 

Physiographic  provinces  of  United 
States,  382. 

Pictet,  F.  J.,  260. 

Piedmont  Plateau,  45,  53,  82,  86-87, 
90,  251,  292. 

Pirsson  and  Schuchert,  33. 

Pithecanthropus,  327,  374-375. 

Pittsburg  coal  bed,  106. 

Placentals,  318. 

Placenticeras,  260. 

Plaesiomys,  95. 

Planetesimal  hypothesis,  37-39. 

Planets,  35-36. 

Plants,  classification,  11-14;  earliest 
forms,  70-71;  Cambrian,  71;  Or- 
dovician,  91;  Silurian,  113;  Devo- 
nian, 132-133;  Mississippian,  153- 
154;  Pennsylvanian,  169-172;  Per- 
mian, 190;  Triassic,  212-213; 
Jurassic,  227-228;  Cretaceous, 
256-258;  Tertiary,  311-313. 

Platyceras,  136. 

Plectambonites,  95. 

Plectorthis,  95. 

Pleistocene  epoch  (see  Glacial  epoch). 

Plesiosaurs,  263,  265-266. 

Pleurocystis,  93. 

Pleuromaria,  136. 

Pliocene  series,  281-282,  284,  286- 
287,  289-290. 

Pocono  sandstone,  143,  145,  148. 

Podokesaurus,  271. 

Porifers,  13,  15;  Cambrian,  72; 
Ordovician,  91;  Silurian,  113-114; 
Devonian,  133;  Mississippian,  155; 
Pennsylvanian,  173;  Permian,  191; 
Triassic,  213;  Jurassic,  228;  Cre- 
taceous, 258;  Tertiary,  313. 

Portage  formation,  120,  124. 

Potomac  series,  244,  276. 

Potsdam  sandstone,  57,  62. 

Pottsville  series,  158,  161-163. 

Poughquag  quartzite,  57. 

Primates,  319,  326-327. 

Proboscidians,  319,  322-325,  371. 

Productus,  135,  156. 


Proterozoic  (see  also  Algonkian)  era, 
32,  42,  47-55;  life  of,  53-54; 
climate,  55;  glaciation,  55;  eco- 
nomic products,  55. 

Protohippus,  320-321. 

Protorohippus,  320. 

Protozoans,  13-15;  Cambrian,  71- 
72;  Ordovician,  91;  Silurian,  113; 
Devonian,  133;  Mississippian,  154; 
Pennsylvanian,  172-173;  Permian, 
190;  Triassic,  213;  Jurassic,  228; 
Cretaceous,  258;  Tertiary,  313. 

Pseudodiadema,  229. 

Pterichthys,  138. 

Pteridophytes,  11,  133,  154,  170-172, 
212. 

Pterodactyls,  263-271. 

Pterosaurs,  215,  234,  263,  271-272. 

Pulaski  formation,  78. 

Pyrenees  Mountains,  305,  306,  307, 
368. 

Quaternary  period,  32,  328-381; 
origin  of  name,  328;  Glacial  epoch, 
328-364  (see  also  special  heading); 
non-glaciated  regions,  365-367;  life 
of,  369-381;  Mammals  (except 
Man),  369-372;  Man,  372-381. 

Quebec,  122,  125. 

Quicksilver,  227. 

Radiolarians,  13,  15,  53,  72,  91,  133, 
154,  190,  228. 

Rancocas  formation,  237,  241. 

Raritan  formation,  237,  240. 

Recapitulation,  law  of,  232-233. 

Recent  epoch,  328. 

"Red  Beds,"  181-182,  188,  194,  197, 
204,  205,  210,  211,  220,  221,  274. 

References,  general  geological,  33-34. 

Reptiles,  13,  22;  Pennsylvanian,  173, 
179;  Permian,  192-193;  Triassic, 
215-216;  Jurassic,  233;  Creta- 
ceous, 262;  Mesozoic,  263-273; 
Tertiary,  317. 

Republican  River  formation,  282, 
289. 

Restinson,  304. 


396 


INDEX 


Rhamphorhyncus,  263,  271-272. 

Rhinoceros,  4. 

Rhizocarps,  133. 

Rhizopods,  13,  14. 

Rhode  Island,  163,  187. 

Ries,  H.,  164. 

Ripley  formation,  237,  241-242. 

Rivet,  E.,  376. 

Rock  scale,  31. 

Rocky  Mountain  district,  50,  53,  58, 

63,  104,  148,   163,   195,  204,  220, 

221,  240,  242,  246,  249,  276,  277, 

289,  301-304. 
Rocky   Mountain   Revolution,    248- 

250,  277. 

Rodents,  319,  325,  371. 
Rondout  formation,  103,  110. 
Ruedemann,  R.,  91,  92,  95,  96,  116. 
Russell,  I.  C.,  367. 
Russia,  68,  111,  132,  152,  167,  180, 

188,  210,  254,  368. 

Salamanders,  13,  22,  317. 

Salina  formation,  103,  106-108,  110, 

112. 

Salisbury,  R.  D.,  29,  330. 
Salisbury  and  Chamberlin  (see  Cham- 

berlin  and  Salisbury). 
Salisbury  and  Willis,  33.  . 
Salt,  106,  110,  112,  153,  188,  190. 
Salter,  J.  W.,  96. 
San  Diego  formation,  282. 
Sandstone  quarries,  69,  112,  212. 
San  Juan  formation,  282,  287. 
San  Lorenzo  formation,  282. 
San  Pablo  formation,  282. 
Santa  Margarita  formation,  282. 
Saratogan  series,  57. 
Sardinia,  67. 

Sauropods,  263,  266-268. 
Say,  114. 

Scandinavia,  45,  53,  68,  111,  254,  368. 
Schoharie  formation,  120,  122. 
Schuchert,  C.,  15,  16,  18,  19,  20,  30, 

54,  126,  175,  196,  232. 
Schuchert  and  Pirsson,  33. 
Scorpions,  13,  21,  117-118,  136,  175- 

176. 


Scotland,  45,  53,  152,  157,  307. 

Scott,  D.  H.,  13,  174. 

Scott,  W.  B.,  6,  7,  8,  33,  76,  101,  125, 
155,  192,  213,  233,  267,  324,  369, 
370. 

Sea-cucumbers,  13,  18,  73. 

Sea-mosses,  13. 

Sea  transgressions,  28;  retrogres- 
sions, 28. 

Sea-urchins,  13,  17,  18,  115,  134. 

Sea-weeds,  91,  113,  132-133,  212. 

Sedgwick,  A.,  56,  77,  120. 

Seed-ferns  (see  also  Cycadofilices), 
11,  133,  154,  172-174. 

Selachians  (see  also  Sharks),  138- 
139,  157,  215,  232. 

Selma  formation,  237,  241,  248. 

Senecan  series,  120,  124;   time,  130. 

Senonian  formation,  237. 

Sequoias,  256,  313. 

Series,  31. 

Sharks  (see  also  Selachians),  119, 
138-139,  157,  261,  316-317. 

Shattuck,  G.  B.,  292,  365. 

Shawangunk  formation,  103,  106- 
108;  Range,  106,  108. 

Shinier,  H.  W.,  14,  17,  18,  21,  34,  73, 
234,  257,  318. 

Shumard,  155. 

Siberia,  68,  89,  90,  132,  200,  210, 
225,  255,  371. 

Sierra  Nevada  Mountains,  220,  223, 
277,  289,  300,  301,  304,  305. 

Sierra  Nevada  Revolution,  223,  277. 

Sigillarians,  170-171,  173,  212. 

Silurian  period,  32,  103-119;  origin 
of  name,  103;  subdivisions,  103; 
rock  distribution,  104-105;  char- 
acter of  rocks,  104-107;  thickness, 
107;  physical  history,  107-110; 
foreign,  111-112;  climate,  112; 
economic  products,  112-113;  life 
of,  113-119. 

Sinclair,  W.  J.,  288,  324. 

Slate,  69. 

Smith,  G.  O.,  303. 

Smith,  J.  P.,  214. 

Smith,  William,  6,  7,  219. 


INDEX 


397 


Smith,  W.  S.,  227. 

Smith  and  Verrill,  18. 

Snails,  13,  20. 

Snakes,  13,  22,  262,  273. 

Solar  system,  35-36. 

Solenhofen  limestone,  225,  234. 

South  America,  9,  132,  168,  171,  210, 

225,  255,  306,  308,  309,  371. 
South   Dakota,    181,  190,  220,  284, 

288,  356. 
Spain,  46,  53,  67,  132,  210,  255,  307, 

379,  380. 

Sphserexochus,  115. 
Spiders,  13,  21,  175-176. 
Spiral  nebula,  37-39. 
Spirifers,  117,  135,  156. 
Sponges   (see  also  Porifers),   13,   15, 

72,    91,    113-114,    133,    155,    173, 

228,  258. 

Spy,  Men  of,  374,  375,  377. 
Squids,  13,  21. 
Stage,  31. 

Star-fishes,  13,  17,  115,  134. 
Staurocephalus,  115. 
Stegocephalians,  157,  178. 
Stegosaurs,  263,  267-269. 
Stephenson,   L.   W.,   241,*  242,   248, 

259,  286,  291-292,  314. 
Stissing  limestone,  57. 
St.  Lawrence  Valley,  63,  88,  104,  144, 

299,  332,  335,  336,  348,  364. 
St.  Louis  series,  143,  147;  time,  148. 
St.  Marys  formation,  282. 
Stoek,  H.,  160. 
Stratigraphy,  defined,  23. 
Stropheodonta,  135. 
Submergence,  of  land,  28. 
Sulphur  deposits,  256. 
Sun,  35-38. 

Superposition,  order  of,  7. 
Susquehanna,  River,  297. 
Sweden,  67,  115,  368. 
Switzerland,  132. 
Syria,  308. 
System,  31,  32. 

Taconic  Range,  86-88,  107,  206. 
Taconic  Revolution,  86-88,  197. 


Talbot,  M.,  figure,  271.- 

Tarr,  R.  S.,  34,  342. 

Tasmania,  68,  89,  152,  188. 

Taylor,  F.  B.,  343,  344,  345,  346,  347. 

Taylor  formation,  237,  242. 

Tejon  formation,  282. 

Teleosts,  140,  232-233,  261,  316. 

Tennessee,  82,  83,  88,  90,  106,  122, 
130,  132. 

Terebratula,  257. 

Tertiary  period,  32,  281-327;  origin 
of  name,  281;  subdivisions,  281- 
282;  rock  distribution,  283-284; 
character  of  rocks,  284-291;  thick- 
ness, 290-291;  igneous  rocks,  291; 
physical  history,  291-304;  igneous 
activity,  303-304;  foreign  Eocene, 
305-306;  foreign  Oligocene,  306- 
307;  foreign  Miocene,  307-309; 
foreign  Pliocene,  308-309;  climate, 
309-310;  economic  products,  310- 
311;  life  of,  311-327. 

Tetrabeledon,  324-325. 

Tetrabranchs,  13,  20,  97-99. 

Tetracoralla,  92,  191,  213. 

Tetragraptus,  92. 

Texas,  53,  58,  106,  128,  160,  169, 
180-182,  190,  219,  242,  244,  246, 
256,  275,  284,  287,  289,  292. 

Thallophytes,  11,  153,  170,  212. 

Theropods,  263,  270-271. 

Thibet,  305. 

Thrimax,  312. 

Till,  339. 

Time  scale,  geological,  31. 

Torridon  sandstone,  53. 

Toxaceras,  260. 

Tracks  of  animals  (see  footprints). 

Traquair,  R.,  137,  139. 

Tremataspis,  138. 

Trent  formation,  282. 

Trenton  formation,  78,  81,  82,  90,  91. 

Triarthrus,  101. 

Triassic  period,  32,  201-218;  origin 
of  name,  201;  subdivisions,  201; 
rock  distribution,  201-203;  char- 
acter of  rocks,  203-206;  thickness, 
206;  igneous  rocks,  206;  physical 


398 


INDEX 


history,    206-210;     foreign,    210; 

climate,  211;    economic  products, 

212;   life  of,  212-218. 
Tribes  Hill  formation,  78. 
Triceratops,  262-263,  268-270. 
Trilobites,   57,    75-76,   99-101,    115, 

117-118,  136-137,  157,  175,  191. 
Trinity,    formation,    237,    242,    276; 

time,  244. 
Trinucleus,  101. 
Trochoceras,  97-99. 
Trocholites,  97-99. 
Troost,  114. 
Troostocrinus,  114. 
Tully  formation,  120,  124. 
Turkestan,  225. 
Turonian  formation,   237. 
Turtles,  216,  234,  273. 
Tuscaloosa  formation,  237,  241. 

Uinta  formation,  282,  287. 

Uinta  Mountains,  82. 

Uintatherium,  318. 

Ulrich,  E.  O.,  18,  65,  154. 

Ulsterian  series,  120,  122;  time, 
128. 

Unconformities,  significance  of,  27; 
Archean-Algonkian,  47;  base  of 
Cambrian,  61. 

Underground  water,  256. 

United  States,  Physiographic  prov- 
inces of,  382. 

Unkar  group,  51. 

Upper  Carboniferous  period  (see 
Pennsylvanian) . 

Ural  Mountains,  305,  306. 

Utah,  181-183,  266,  287,  304,  366. 

Utica  formation,  78,  82. 

Valley  trains,  338. 

Van  Hise  and  Leith,  41,  48,  51. 

Vanuxem,  L.,  96. 

Vaqueros  formation,  282. 

Vaughn,  T.  W.,  229,  230,  259. 

Veatch,  A.  C.,  316. 

Vermes,  13,  18. 

Vermont,  59,  69. 

Verrill  and  Smith,  18. 


Vertebrates,   13,  21,   100,   119,   136, 

157,  177-179,  191-193. 
Vicksburg  formation,  282,  287. 
Vinci,  Leonardo  da,  6. 
Virginia,  86,  110,  145,  153,  164,  187, 

203,  212,  213,  251,  256,  312,  371. 
Voltzia,  213. 

Waagenoceras,  99,  191. 

Waccamaw  formation,  282,  286,  291. 

Walcott,  C.  D.,  53,  54,  61,  65,  71, 

73,  74,  76. 

Wales,  56,  67,  68,  69,  103. 
Ward,  L.,  228. 

Wasatch  formation,  282,  287. 
Wasatch   Mountains,    82,    181,    183, 

220,  301. 

Washington,  223,  289,  303. 
Washita    formation,  237,    242,  276; 

time,  246. 
Wasps,  232. 
Waterlime,  112. 
Waucobian  series,  57. 
Well  records,  diagram,  60. 
West  Virginia,  132,  147,  153,  169, 181. 
Whales,  evolution  of,  325-326. 
White,  D.,:  161,  168,  171. 
White  Mountains,  86,  87,  250,  332, 

372. 

White  River  formation,  282,  287-288. 
Wichita  Mountains,  82,  86. 
Wichita  series,  180. 
Wilcox  formation,  282. 
Willis,  Bailey,  30,  33,  44,  58,  64,  66, 

68,  85,  105,  109,  123,  127,  145,  146, 

149,  159,  165,  184,  202,  207,  222, 

238,  239,  245,  247,  283,  285,  293, 

295. 

Willis  and  Salisbury,  33. 
Williston,  S.  W.,  173,  178-179. 
Wind  River  formation,  282,  287. 
Wisconsin,  55,  90,  105-107,  110,  115, 

128,  334,  339,  340. 
Wissler,  C.,  374,  379-380. 
Woodbine,  formation,  237,  242;  time, 

246 

Woods,  34. 
Woodward,  138,  139,  378. 


INDEX  399 

Worms,  13,  18,  53,  73.  Yorktown  formation,  282. 

Worthen,  A.  H.,  176.  Yosemite  Valley,  301. 
Wyoming,  65,  84,  102,  160,  164,  181, 

182,  205,  220,  242,  256,  287,  288,  Zaphrentis,  113. 

303.  Zinc  ore,  90,  153. 

Zittel,  Carl,  13. 

Yellowstone  Park,  303.  Zittel-Eastman,  34. 


D.  VAN  NOSTRAND  COMPANY 

are  prepared  to  supply,  either  from 

their  complete  stock  or  at 

short  notice, 

Any  Technical  or 

Scientific  Book 

In  addition  to  their  own  extensive 
list  of  publications  embracing  every 
branch  of  SCIENCE,  TECHNOLOGY 
and  ENGINEERING,  D.  Van  Nostrand 
Company  have  on  hand  the  largest 
assortment  in  the  United  States  of 
such  books  issued  by  American  and 
foreign  publishers. 


All  inquiries  are  cheerfully  and  care- 
fully answered  and  complete  catalogs 
sent  free  on  request. 


25  PARK  PLACE  ...       NEW  YORK 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROW® 

LOAN  DEPT. 

^^itt^assa?* 

Renewed  books  are  subject  to  immediate  n 


LD  21A-50W-11/62 
(D3279slO)476B 


General  Library     . 
University  of  California 
Berkeley 


YB   Ic 


D  /Go 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


